Hypothetical reference decoder parameters in video coding

ABSTRACT

A device performs a hypothetical reference decoder (HRD) operation that determines conformance of a bitstream to a video coding standard or determines conformance of a video decoder to the video coding standard. As part of performing the HRD operation, the device determines a highest temporal identifier of a bitstream-subset associated with a selected operation point of the bitstream. Furthermore, as part of the HRD operation, the device determines, based on the highest temporal identifier, a particular syntax element from among an array of syntax elements. The device then uses the particular syntax element in the HRD operation.

This application claims the benefit of U.S. Provisional PatentApplication No. 61/705,102, filed Sep. 24, 2012, the entire content ofwhich is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and decoding (i.e., encodingand/or decoding of video data).

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocompression techniques, such as those described in the standards definedby MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, AdvancedVideo Coding (AVC), the High Efficiency Video Coding (HEVC) standardpresently under development, and extensions of such standards. The videodevices may transmit, receive, encode, decode, and/or store digitalvideo information more efficiently by implementing such videocompression techniques.

Video compression techniques perform spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (i.e., a video frame or a portion of a video frame) may bepartitioned into video blocks. Video blocks in an intra-coded (I) sliceof a picture are encoded using spatial prediction with respect toreference samples in neighboring blocks in the same picture. Videoblocks in an inter-coded (P or B) slice of a picture may use spatialprediction with respect to reference samples in neighboring blocks inthe same picture or temporal prediction with respect to referencesamples in other reference pictures. Pictures may be referred to asframes, and reference pictures may be referred to a reference frames.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicates the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual coefficients, which then may be quantized. The quantizedcoefficients, initially arranged in a two-dimensional array, may bescanned in order to produce a one-dimensional vector of coefficients,and entropy coding may be applied to achieve even more compression.

A multi-view coding bitstream may be generated by encoding views, e.g.,from multiple perspectives. Some three-dimensional (3D) video standardshave been developed that make use of multiview coding aspects. Forexample, different views may transmit left and right eye views tosupport 3D video. Alternatively, some 3D video coding processes mayapply so-called multiview plus depth coding. In multiview plus depthcoding, 3D video bitstream may contain not only texture view components,but also depth view components. For example, each view may comprise onetexture view component and one depth view component.

SUMMARY

In general, this disclosure describes signaling and selection ofhypothetical reference decoder (HRD) parameters in video coding. Morespecifically, a device performs a hypothetical reference decoder (HRD)operation that determines conformance of a bitstream to a video codingstandard or determines conformance of a video decoder to the videocoding standard. As part of performing the HRD operation, the devicedetermines a highest temporal identifier of a bitstream-subsetassociated with a selected operation point of the bitstream.Furthermore, as part of the HRD operation, the device determines, basedon the highest temporal identifier, a particular syntax element fromamong an array of syntax elements. The device then uses the particularsyntax element in the HRD operation.

In one example, this disclosure describes a method of processing videodata. The method comprises performing a HRD operation. The HRD operationdetermines conformance of a bitstream to a video coding standard ordetermines conformance of a video decoder to the video coding standard.Performing the HRD operation comprises determining a highest temporalidentifier of a bitstream-subset associated with a selected operationpoint of the bitstream. Performing the HRD operation also comprisesdetermining, based on the highest temporal identifier, a particularsyntax element from among an array of syntax elements. In addition,performing the HRD operation comprises using the particular syntaxelement in the HRD operation.

In another example, this disclosure describes a device comprising one ormore processors configured to perform a HRD operation. The HRD operationdetermines conformance of a bitstream to a video coding standard ordetermines conformance of a video decoder to the video coding standard.Performing the HRD operation comprises determining a highest temporalidentifier of a bitstream-subset associated with a selected operationpoint of the bitstream. Performing the HRD operation also comprisesdetermining, based on the highest temporal identifier, a particularsyntax element from among an array of syntax elements. In addition,performing the HRD operation comprises using the particular syntaxelement in the HRD operation.

In another example, this disclosure describes a device comprising meansfor performing a HRD operation. The HRD operation determines conformanceof a bitstream to a video coding standard or determines conformance of avideo decoder to the video coding standard. Performing the HRD operationcomprises determining a highest temporal identifier of abitstream-subset associated with a selected operation point of thebitstream. Performing the HRD operation also comprises determining,based on the highest temporal identifier, a particular syntax elementfrom among an array of syntax elements. In addition, performing the HRDoperation comprises using the particular syntax element in the HRDoperation.

In another example, this disclosure describes a computer-readablestorage medium having instructions stored thereon that, when executed byone or more processors of a device, configure the device to perform aHRD operation. The HRD operation determines conformance of a bitstreamto a video coding standard or determines conformance of a video decoderto the video coding standard. Performing the HRD operation comprisesdetermining a highest temporal identifier of a bitstream-subsetassociated with a selected operation point of the bitstream. Inaddition, performing the HRD operation comprises determining, based onthe highest temporal identifier, a particular syntax element from amongan array of syntax elements. Furthermore, performing the HRD operationcomprises using the particular syntax element in the HRD operation.

The details of one or more examples of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description, drawings,and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video coding systemthat may utilize the techniques described in this disclosure.

FIG. 2 is a block diagram illustrating an example video encoder that mayimplement the techniques described in this disclosure.

FIG. 3 is a block diagram illustrating an example video decoder that mayimplement the techniques described in this disclosure.

FIG. 4 is a flowchart illustrating an example operation of a device, inaccordance with one or more techniques of this disclosure.

FIG. 5 is a flowchart illustrating an example operation of a device, inaccordance with one or more techniques of this disclosure.

FIG. 6 is a flowchart illustrating an example hypothetical referencedecoder (HRD) operation of a device, in accordance with one or moretechniques of this disclosure.

DETAILED DESCRIPTION

A video encoder may generate a bitstream that includes encoded videodata. The bitstream may comprise a series of network abstraction layer(NAL) units. The NAL units of the bitstream may include video codinglayer (VCL) NAL units and non-VCL NAL units. The VCL NAL units mayinclude coded slices of pictures. A non-VCL NAL unit may include a videoparameter set (VPS), a sequence parameter set (SPS), a picture parameterset (PPS), supplemental enhancement information (SEI), or other types ofdata. A VPS is a syntax structure that may contain syntax elements thatapply to zero or more entire coded video sequences. A SPS is a syntaxstructure that may contain syntax elements that apply to zero or moreentire coded video sequences. A single VPS may be applicable to multipleSPS's. A PPS is a syntax structure that may contain syntax elements thatapply to zero or more entire coded pictures. A single SPS may beapplicable to multiple PPS's. Various aspects of the VPS, SPS and PPSmay be formed, in general, as defined by the HEVC standard.

A device, such as a content delivery network (CDN) device, a Media-AwareNetwork Element (MANE), or a video decoder, may extract a sub-bitstreamfrom the bitstream. The device may perform the sub-bitstream extractionprocess by removing certain NAL units from the bitstream. The resultingsub-bitstream includes the remaining, non-removed NAL units of thebitstream. As examples, video data decoded from the sub-bitstream mayhave a lower frame rate and/or may represent fewer views than theoriginal bitstream.

Video coding standards may include various features to support thesub-bitstream extraction process. For example, video data of thebitstream may be divided into a set of layers. For each of the layers,data in a lower layer may be decoded without reference to data in anyhigher layer. An individual NAL unit only encapsulates data of a singlelayer. Thus, NAL units encapsulating data of the highest remaining layerof the bitstream may be removed from the bitstream without affecting thedecodability of data in the remaining lower layers of the bitstream. Inscalable video coding (SVC), higher layers may include enhancement datathat improve the quality of pictures in lower layers (qualityscalability), enlarge the spatial format of pictures in lower layers(spatial scalability), or increase the temporal rate of pictures inlower layers (temporal scalability). In multi-view coding (MVC) andthree-dimensional video (3DV) coding, higher layers may includeadditional views.

NAL units may include headers and payloads. The headers of NAL unitsinclude nuh_reserved_zero_(—)6 bits syntax elements. Thenuh_reserved_zero_(—)6 bits syntax element of a NAL unit is equal to 0if the NAL unit relates to a base layer in multi-view coding, 3DVcoding, or SVC. Data in a base layer of a bitstream may be decodedwithout reference to data in any other layer of the bitstream. If theNAL unit does not relate to a base layer in multi-view coding, 3DV, orSVC, the nuh_reserved_zero_(—)6 bits syntax element may have a non-zerovalue. Specifically, if a NAL unit does not relate to a base layer inmulti-view coding, 3DV, or SVC, the nuh_reserved_zero_(—)6 bits syntaxelement of the NAL unit specifies a layer identifier of the NAL unit.

Furthermore, some pictures within a layer may be decoded withoutreference to other pictures within the same layer. Thus, NAL unitsencapsulating data of certain pictures of a layer may be removed fromthe bitstream without affecting the decodability of other pictures inthe layer. For example, pictures with even picture order count (POC)values may be decodable without reference to pictures with odd POCvalues. Removing NAL units encapsulating data of such pictures mayreduce the frame rate of the bitstream. A subset of pictures within alayer that may be decoded without reference to other pictures within thelayer may be referred to herein as a sub-layer.

NAL units may include temporal_id syntax elements. The temporal_idsyntax element of a NAL unit specifies a temporal identifier of the NALunit. If the temporal identifier of a first NAL unit is less than thetemporal identifier of a second NAL unit, the data encapsulated by thefirst NAL unit may be decoded without reference to the data encapsulatedby the second NAL unit.

Each operation point of a bitstream is associated with a set of layeridentifiers (i.e., a set of nuh_reserved_zero_(—)6 bits values) and atemporal identifier. The set of layer identifiers may be denoted asOpLayerIdSet and the temporal identifier may be denoted as TemporalID.If a NAL unit's layer identifier is in an operation point's set of layeridentifiers and the NAL unit's temporal identifier is less than or equalto the operation point's temporal identifier, the NAL unit is associatedwith the operation point. An operation point representation is abitstream subset that is associated with an operation point. Theoperation point representation may include each NAL unit that isassociated with the operation point. The operation point representationdoes not include VCL NAL units that are not associated with theoperation point.

An external source may specify a set of target layer identifiers for anoperation point. For example, a device, such as a CDN device or a MANE,may specify the set of target layer identifiers. In this example, thedevice may use the set of target layer identifiers to identify anoperation point. The device may then extract the operation pointrepresentation for the operation point and forward the operation pointrepresentation, instead of the original bitstream, to a client device.Extracting and forwarding the operation point representation to theclient device may reduce the bit rate of the bitstream.

Furthermore, video coding standards specify video buffering models. Avideo buffering model may also be referred to as a “hypotheticalreference decoder” or an “HRD.” The HRD describes how data is to bebuffered for decoding and how decoded data is buffered for output. Forinstance, the HRD describes the operation of a coded picture buffer(“CPB”) and a decoded picture buffer (“DPB”) in a video decoder. The CPBis a first-in first-out buffer containing access units in decoding orderspecified by HRD. The DPB is a buffer holding decoded pictures forreference, output reordering, or output delay specified by the HRD.

A video encoder may signal a set of HRD parameters. The HRD parameterscontrol various aspects of the HRD. The HRD parameters include aninitial CPB removal delay, a CPB size, a bit rate, an initial DPB outputdelay, and a DPB size. These HRD parameters are coded in ahrd_parameters( ) syntax structure specified in a VPS and/or a SPS. TheHRD parameters can also be specified in a buffering period supplementalenhancement information (SEI) message or a picture timing SEI message.

As explained above, an operation point representation may have adifferent frame rate and/or bit rate than an original bitstream. This isbecause the operation point representation may not include some picturesand/or some of the data of the original bitstream. Hence, if the videodecoder were to remove data from the CPB and/or the DPB at a particularrate when processing the original bitstream and if the video decoderwere to remove data from the CPB and/or the DPB at the same rate whenprocessing an operation point representation, the video decoder mayremove too much or too little data from the CPB and/or the DPB.Accordingly, the video encoder may signal different sets of HRDparameters for different operation points. In the emergingHigh-Efficiency Video Coding (HEVC) standard, the video encoder maysignal sets of HRD parameters in a VPS or the video encoder may signalsets of HRD parameters in a SPS. A draft of the upcoming HEVC standard,referred to as “HEVC Working Draft 8” is described in Bross et al.,“High Efficiency Video Coding (HEVC) text specification draft 8,” JointCollaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 andISO/IEC JTC1/SC29/WG11, 10^(th) Meeting, Stockholm, Sweden, July 2012,which as of May 8, 2013, is available fromhttp://phenix.int-evry.fr/jct/doc_end_user/documents/10_Stockholm/wg11/JCTVC-J1003-v8.zip.

In some versions of HEVC, only the sets of HRD parameters in the VPS areselected for HRD operations. That is, although HRD parameters can beprovided in SPS's, the sets of HRD parameters in the SPS's are notselected by HEVC video decoders for HRD operations. Video decodersalways parse and decode the VPS of a bitstream. Hence, video decodersalways parse and decode the sets of HRD parameters of the VPS. This istrue regardless of whether the bitstream includes non-base layer NALunits. Hence, if the bitstream includes non-base layer NAL units, it maybe a waste of computational resources to parse and handle the sets ofHRD parameters in the SPS's. Furthermore, if the sets of HRD parametersare present in the VPS, the sets of HRD parameters in the SPS's may bewasted bits.

In accordance with the techniques of this disclosure, a video encodermay generate a bitstream that includes a SPS that is applicable to asequence of pictures. The SPS includes a set of HRD parameters. The setof HRD parameters is applicable to each operation point of the bitstreamthat has a set of layer identifiers that match a set of target layeridentifiers. Thus, the sets of HRD parameters in the SPS's are notwasted, but rather may be used for HRD operations. For instance, adevice may select, from among a set of HRD parameters in a VPS and a setof HRD parameters in a SPS, a set of HRD parameters applicable to aparticular operation point. The device may perform, based at least inpart on the set of HRD parameters applicable to the particular operationpoint, a bitstream conformance test that tests whether a bitstreamsubset associated with the particular operation point conforms to avideo coding standard.

A device, such as a video encoder, a video decoder, or another type ofdevice, such as a CDN device or MANE, may perform a bitstreamconformance test on an operation point representation for an operationpoint. The bitstream conformance test may verify that the operationpoint representation conforms to a video coding standard, such as HEVC.As mentioned above, a set of target layer identifiers and a temporalidentifier may be used to identify the operation point. The set oftarget layer identifiers may be denoted as “TargetDecLayerIdSet.” Thetemporal identifier may be denoted as “TargetDecHighestTid.”Problematically, HEVC Working Draft 8 does not specify howTargetDecLayerIdSet or TargetDecHighestTid are set when performing abitstream conformance test.

In accordance with one or more techniques of this disclosure, a devicemay perform a decoding process as part of performing a bitstreamconformance test. Performing the decoding process comprises performing abitstream extraction process to decode, from a bitstream, an operationpoint representation of an operation point defined by a target set oflayer identifiers and a target highest temporal identifier. The targetset of layer identifiers (i.e., TargetDecLayerIdSet) contains values oflayer identifier syntax elements (e.g., nuh_reserved_zero_(—)6 bitssyntax elements) present in the operation point representation. Thetarget set of layer identifiers is a subset of values of layeridentifier syntax elements of the bitstream. The target highest temporalidentifier (i.e., TargetDecHighestTid) is equal to a greatest temporalidentifier present in the operation point representation. The targethighest temporal identifier is less than or equal to a greatest temporalidentifier present in the bitstream. Performing the decoding process mayalso comprise decoding NAL units of the operation point representation.

In HEVC, a SPS may include an array of syntax elements denoted assps_max_dec_pic_buffering[i], where i ranges from 0 to the maximumnumber of temporal layers in the bitstream. sps_max_dec_pic_buffering[i]indicates the maximum required size of the DPB when a highest temporalidentifier (HighestTid) is equal to i. sps_max_dec_pic_buffering[i]indicates the required size in terms of units of picture storagebuffers.

Furthermore, in HEVC, a SPS may include an array of syntax elementsdenoted sps_max_num_reorder_pics[i], where i ranges from 0 to themaximum number of temporal layers in the bitstream.sps_max_num_reorder_pics[i] indicates a maximum allowed number ofpictures preceding any picture in decoding order and succeeding thatpicture in output order when a highest temporal identifier (HighestTid)is equal to i.

In HEVC, a set of HRD parameters may include an array of syntax elementsdenoted cpb_cnt_minus1[i], where i ranges from 0 to the maximum numberof temporal layers in the bitstream. cpb_cnt_minus1[i] specifies thenumber of alternative CPB specifications in the bitstream of the codedvideo sequence when a highest temporal identifier (HighestTid) is equalto i, wherein one alternative CPB specification refers to one particularCPB operation with a particular set of CPB parameters.

In HEVC Working Draft 8, sps_max_dec_pic_buffering[i],sps_max_num_reorder_pics[i], and cpb_cnt_minus1[i] are not properlyselected in HRD operations, bitstream conformance operations, and levelrestrictions. This is at least in part because HEVC Working Draft 8 doesnot specify what is meant by the highest temporal identifier(HighestTid).

In accordance with one or more techniques of this disclosure, a device,such as a video encoder, a video decoder, or another device, maydetermine a highest temporal identifier of a bitstream-subset associatedwith a selected operation point of a bitstream. Furthermore, the devicemay determine, based on the highest temporal identifier, a particularsyntax element from among an array of syntax elements (e.g.,sps_max_dec_pic_buffering[ ], sps_max_num_reorder_pics[ ], orcpb_cnt_minus1[ ]). The device may perform an operation that uses theparticular syntax element to determine conformance of the bitstream to avideo coding standard or to determine conformance of a video decoder tothe video coding standard.

FIG. 1 is a block diagram illustrating an example video coding system 10that may utilize the techniques of this disclosure. As used herein, theterm “video coder” refers generically to both video encoders and videodecoders. In this disclosure, the terms “video coding” or “coding” mayrefer generically to video encoding or video decoding.

As shown in FIG. 1, video coding system 10 includes a source device 12and a destination device 14. Source device 12 generates encoded videodata. Accordingly, source device 12 may be referred to as a videoencoding device or a video encoding apparatus. Destination device 14 maydecode the encoded video data generated by source device 12.Accordingly, destination device 14 may be referred to as a videodecoding device or a video decoding apparatus. Source device 12 anddestination device 14 may be examples of video coding devices or videocoding apparatuses.

Source device 12 and destination device 14 may comprise a wide range ofdevices, including desktop computers, mobile computing devices, notebook(e.g., laptop) computers, tablet computers, set-top boxes, telephonehandsets such as so-called “smart” phones, televisions, cameras, displaydevices, digital media players, video gaming consoles, in-car computers,or the like.

Destination device 14 may receive encoded video data from source device12 via a channel 16. Channel 16 may comprise one or more media ordevices capable of moving the encoded video data from source device 12to destination device 14. In one example, channel 16 may comprise one ormore communication media that enable source device 12 to transmitencoded video data directly to destination device 14 in real-time. Inthis example, source device 12 may modulate the encoded video dataaccording to a communication standard, such as a wireless communicationprotocol, and may transmit the modulated video data to destinationdevice 14. The one or more communication media may include wirelessand/or wired communication media, such as a radio frequency (RF)spectrum or one or more physical transmission lines. The one or morecommunication media may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network (e.g., theInternet). The one or more communication media may include routers,switches, base stations, or other equipment that facilitatecommunication from source device 12 to destination device 14.

In another example, channel 16 may include a storage medium that storesencoded video data generated by source device 12. In this example,destination device 14 may access the storage medium, e.g., via diskaccess or card access. The storage medium may include a variety oflocally-accessed data storage media such as Blu-ray discs, DVDs,CD-ROMs, flash memory, or other suitable digital storage media forstoring encoded video data.

In a further example, channel 16 may include a file server or anotherintermediate storage device that stores encoded video data generated bysource device 12. In this example, destination device 14 may accessencoded video data stored at the file server or other intermediatestorage device via streaming or download. The file server may be a typeof server capable of storing encoded video data and transmitting theencoded video data to destination device 14. Example file serversinclude web servers (e.g., for a website), file transfer protocol (FTP)servers, network attached storage (NAS) devices, and local disk drives.In the example of FIG. 1, channel 16 includes an additional device 21.In some examples, additional device 21 is a CDN device, a MANE, oranother type of device.

Destination device 14 may access the encoded video data through astandard data connection, such as an Internet connection. Example typesof data connections may include wireless channels (e.g., Wi-Ficonnections), wired connections (e.g., digital subscriber line (DSL),cable modem, etc.), or combinations of both that are suitable foraccessing encoded video data stored on a file server. The transmissionof encoded video data from the file server may be a streamingtransmission, a download transmission, or a combination of both.

The techniques of this disclosure are not limited to wirelessapplications or settings. The techniques may be applied to video codingin support of a variety of multimedia applications, such as over-the-airtelevision broadcasts, cable television transmissions, satellitetelevision transmissions, streaming video transmissions, e.g., via theInternet, encoding of video data for storage on a data storage medium,decoding of video data stored on a data storage medium, or otherapplications. In some examples, video coding system 10 may be configuredto support one-way or two-way video transmission to support applicationssuch as video streaming, video playback, video broadcasting, and/orvideo telephony.

FIG. 1 is merely an example and the techniques of this disclosure mayapply to video coding settings (e.g., video encoding or video decoding)that do not necessarily include any data communication between theencoding and decoding devices. In other examples, data is retrieved froma local memory, streamed over a network, or the like. A video encodingdevice may encode and store data to memory, and/or a video decodingdevice may retrieve and decode data from memory. In many examples, theencoding and decoding is performed by devices that do not communicatewith one another, but simply encode data to memory and/or retrieve anddecode data from memory.

In the example of FIG. 1, source device 12 includes a video source 18, avideo encoder 20, and an output interface 22. In some examples, outputinterface 22 may include a modulator/demodulator (modem) and/or atransmitter. Video source 18 may include a video capture device, e.g., avideo camera, a video archive containing previously-captured video data,a video feed interface to receive video data from a video contentprovider, and/or a computer graphics system for generating video data,or a combination of such sources of video data.

Video encoder 20 may encode video data from video source 18. In someexamples, source device 12 directly transmits the encoded video data todestination device 14 via output interface 22. In other examples, theencoded video data may also be stored onto a storage medium or a fileserver for later access by destination device 14 for decoding and/orplayback.

In the example of FIG. 1, destination device 14 includes an inputinterface 28, a video decoder 30, and a display device 32. In someexamples, input interface 28 includes a receiver and/or a modem. Inputinterface 28 may receive encoded video data over channel 16. Displaydevice 32 may be integrated with or may be external to destinationdevice 14. In general, display device 32 displays decoded video data.Display device 32 may comprise a variety of display devices, such as aliquid crystal display (LCD), a plasma display, an organic lightemitting diode (OLED) display, or another type of display device.

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable circuitry, such as one or more microprocessors,digital signal processors (DSPs), application-specific integratedcircuits (ASICs), field-programmable gate arrays (FPGAs), discretelogic, hardware, or any combinations thereof. If the techniques areimplemented partially in software, a device may store instructions forthe software in a suitable, non-transitory computer-readable storagemedium and may execute the instructions in hardware using one or moreprocessors to perform the techniques of this disclosure. Any of theforegoing (including hardware, software, a combination of hardware andsoftware, etc.) may be considered to be one or more processors. Each ofvideo encoder 20 and video decoder 30 may be included in one or moreencoders or decoders, either of which may be integrated as part of acombined encoder/decoder (CODEC) in a respective device.

This disclosure may generally refer to video encoder 20 “signaling”certain information to another device, such as video decoder 30 oradditional device 21. The term “signaling” may generally refer to thecommunication of syntax elements and/or other data used to decode thecompressed video data. Such communication may occur in real- ornear-real-time. Alternately, such communication may occur over a span oftime, such as might occur when storing syntax elements to acomputer-readable storage medium in an encoded bitstream at the time ofencoding, which then may be retrieved by a decoding device at any timeafter being stored to this medium.

In some examples, video encoder 20 and video decoder 30 operateaccording to a video compression standard, such as ISO/IEC MPEG-4 Visualand ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including itsScalable Video Coding (SVC) extension, Multiview Video Coding (MVC)extension, and/or MVC-based 3DV extension. In some instances, anybitstream conforming to MVC-based 3DV always contains a sub-bitstreamthat is compliant to a MVC profile, e.g., stereo high profile.Furthermore, there is an ongoing effort to generate a three-dimensionalvideo (3DV) coding extension to H.264/AVC, namely AVC-based 3DV. Inother examples, video encoder 20 and video decoder 30 may operateaccording to ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IECMPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual, and ITU-T H.264,ISO/IEC Visual.

In other examples, video encoder 20 and video decoder 30 may operateaccording to the High Efficiency Video Coding (HEVC) standard presentlyunder development by the Joint Collaboration Team on Video Coding(JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC MotionPicture Experts Group (MPEG). A draft of the upcoming HEVC standard,referred to as “HEVC Working Draft 9” is described in Bross et al.,“High Efficiency Video Coding (HEVC) text specification draft 9,” JointCollaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 andISO/IEC JTC1/SC29/WG11, 11^(th) Meeting, Shanghai, China, October 2012,which as of May 8, 2013, is available fromhttp://phenix.int-evry.fr/jct/doc_end_user/documents/11_Shanghai/wg11/JCTVC-K1003-v13.zip.Furthermore, there are ongoing efforts to produce SVC, multi-viewcoding, and 3DV extensions for HEVC. The 3DV extension of HEVC may bereferred to as HEVC-based 3DV or 3D-HEVC.

In HEVC and other video coding standards, a video sequence typicallyincludes a series of pictures. Pictures may also be referred to as“frames.” A picture may include three sample arrays, denoted S_(L),S_(Cb) and S_(Cr). S_(L) is a two-dimensional array (i.e., a block) ofluma samples. S_(Cb) is a two-dimensional array of Cb chrominancesamples. S_(Cr) is a two-dimensional array of Cr chrominance samples.Chrominance samples may also be referred to herein as “chroma” samples.In other instances, a picture may be monochrome and may only include anarray of luma samples.

To generate an encoded representation of a picture, video encoder 20 maygenerate a set of coding tree units (CTUs). Each of the CTUs may be acoding tree block of luma samples, two corresponding coding tree blocksof chroma samples, and syntax structures used to code the samples of thecoding tree blocks. A coding tree block may be an N×N block of samples.A CTU may also be referred to as a “tree block” or a “largest codingunit” (LCU). The CTUs of HEVC may be broadly analogous to themacroblocks of other standards, such as H.264/AVC. However, a CTU is notnecessarily limited to a particular size and may include one or morecoding units (CUs). A slice may include an integer number of CTUsordered consecutively in a raster scan.

To generate a coded CTU, video encoder 20 may recursively performquad-tree partitioning on the coding tree blocks of a CTU to divide thecoding tree blocks into coding blocks, hence the name “coding treeunits.” A coding block is an N×N block of samples. A CU may be a codingblock of luma samples and two corresponding coding blocks of chromasamples of a picture that has a luma sample array, a Cb sample array anda Cr sample array, and syntax structures used to code the samples of thecoding blocks. Video encoder 20 may partition coding blocks of a CU intoone or more prediction blocks. A prediction block may be a rectangular(i.e., square or non-square) block of samples on which the sameprediction is applied. A prediction unit (PU) of a CU may be aprediction block of luma samples, two corresponding prediction blocks ofchroma samples of a picture, and syntax structures used to predict theprediction block samples. Video encoder 20 may generate predictive luma,Cb and Cr blocks for luma, Cb and Cr prediction blocks of each PU of theCU.

Video encoder 20 may use intra prediction or inter prediction togenerate the predictive blocks for a PU. If video encoder 20 uses intraprediction to generate the predictive blocks of a PU, video encoder 20may generate the predictive blocks of the PU based on decoded samples ofthe picture associated with the PU.

If video encoder 20 uses inter prediction to generate the predictiveblocks of a PU, video encoder 20 may generate the predictive blocks ofthe PU based on decoded samples of one or more pictures other than thepicture associated with the PU. Video encoder 20 may use uni-predictionor bi-prediction to generate the predictive blocks of a PU. When videoencoder 20 uses uni-prediction to generate the predictive blocks for aPU, the PU may have a single motion vector. When video encoder 20 usesbi-prediction to generate the predictive blocks for a PU, the PU mayhave two motion vectors.

After video encoder 20 generates predictive luma, Cb and Cr blocks forone or more PUs of a CU, video encoder 20 may generate a luma residualblock for the CU. Each sample in the CU's luma residual block indicatesa difference between a luma sample in one of the CU's predictive lumablocks and a corresponding sample in the CU's original luma codingblock. In addition, video encoder 20 may generate a Cb residual blockfor the CU. Each sample in the CU's Cb residual block may indicate adifference between a Cb sample in one of the CU's predictive Cb blocksand a corresponding sample in the CU's original Cb coding block. Videoencoder 20 may also generate a Cr residual block for the CU. Each samplein the CU's Cr residual block may indicate a difference between a Crsample in one of the CU's predictive Cr blocks and a correspondingsample in the CU's original Cr coding block.

Furthermore, video encoder 20 may use quad-tree partitioning todecompose the luma, Cb and Cr residual blocks of a CU into one or moreluma, Cb and Cr transform blocks. A transform block may be a rectangularblock of samples on which the same transform is applied. A transformunit (TU) of a CU may be a transform block of luma samples, twocorresponding transform blocks of chroma samples, and syntax structuresused to transform the transform block samples. Thus, each TU of a CU maybe associated with a luma transform block, a Cb transform block, and aCr transform block. The luma transform block associated with the TU maybe a sub-block of the CU's luma residual block. The Cb transform blockmay be a sub-block of the CU's Cb residual block. The Cr transform blockmay be a sub-block of the CU's Cr residual block.

Video encoder 20 may apply one or more transforms to a luma transformblock of a TU to generate a luma coefficient block for the TU. Acoefficient block may be a two-dimensional array of transformcoefficients. A transform coefficient may be a scalar quantity. Videoencoder 20 may apply one or more transforms to a Cb transform block of aTU to generate a Cb coefficient block for the TU. Video encoder 20 mayapply one or more transforms to a Cr transform block of a TU to generatea Cr coefficient block for the TU.

After generating a coefficient block (e.g., a luma coefficient block, aCb coefficient block or a Cr coefficient block), video encoder 20 mayquantize the coefficient block. Quantization generally refers to aprocess in which transform coefficients are quantized to possibly reducethe amount of data used to represent the transform coefficients,providing further compression. After video encoder 20 quantizes acoefficient block, video encoder 20 may entropy encode syntax elementsindicating the quantized transform coefficients. For example, videoencoder 20 may perform Context-Adaptive Binary Arithmetic Coding (CABAC)on the syntax elements indicating the quantized transform coefficients.Video encoder 20 may output the entropy-encoded syntax elements in abitstream.

Video encoder 20 may output a bitstream that includes a sequence of bitsthat forms a representation of coded pictures and associated data. Thebitstream may comprise a sequence of network abstraction layer (NAL)units. A NAL unit may be a syntax structure containing an indication ofthe type of data to follow and bytes containing that data in the form ofa raw byte sequence payload (RBSP) interspersed as necessary withemulation prevention bytes. That is, each of the NAL units may include aNAL unit header and encapsulate a RBSP. The NAL unit header may includea syntax element that indicates a NAL unit type code. The NAL unit typecode specified by the NAL unit header of a NAL unit indicates the typeof the NAL unit. A RBSP may be a syntax structure containing an integernumber of bytes that is encapsulated within a NAL unit. In someinstances, an RBSP includes zero bits.

Different types of NAL units may encapsulate different types of RBSPs.For example, a first type of NAL unit may encapsulate an RBSP for apicture parameter set (PPS), a second type of NAL unit may encapsulatean RBSP for a coded slice, a third type of NAL unit may encapsulate anRBSP for SEI, and so on. NAL units that encapsulate RBSPs for videocoding data (as opposed to RBSPs for parameter sets and SEI messages)may be referred to as video coding layer (VCL) NAL units.

Video decoder 30 may receive a bitstream generated by video encoder 20.In addition, video decoder 30 may parse the bitstream to decode syntaxelements from the bitstream. Video decoder 30 may reconstruct thepictures of the video data based at least in part on the syntax elementsdecoded from the bitstream. The process to reconstruct the video datamay be generally reciprocal to the process performed by video encoder20. For instance, video decoder 30 may use motion vectors of PUs todetermine predictive blocks for the PUs of a current CU. In addition,video decoder 30 may inverse quantize transform coefficient blocksassociated with TUs of the current CU. Video decoder 30 may performinverse transforms on the transform coefficient blocks to reconstructtransform blocks associated with the TUs of the current CU. Videodecoder 30 may reconstruct the coding blocks of the current CU by addingthe samples of the predictive blocks for PUs of the current CU tocorresponding samples of the transform blocks of the TUs of the currentCU. By reconstructing the coding blocks for each CU of a picture, videodecoder 30 may reconstruct the picture.

In multi-view coding, there may be multiple views of the same scene fromdifferent viewpoints. The term “access unit” is used to refer to the setof pictures that correspond to the same time instance. Thus, video datamay be conceptualized as a series of access units occurring over time. A“view component” may be a coded representation of a view in a singleaccess unit. In this disclosure, a “view” may refer to a sequence ofview components associated with the same view identifier.

Multi-view coding supports inter-view prediction. Inter-view predictionis similar to the inter prediction used in H.264/AVC and HEVC and mayuse the same syntax elements. However, when a video coder performsinter-view prediction on a current video unit (such as a PU), videoencoder 20 may use, as a reference picture, a picture that is in thesame access unit as the current video unit, but in a different view. Incontrast, conventional inter prediction only uses pictures in differentaccess units as reference pictures.

In multi-view coding, a view may be referred to as a “base view” if avideo decoder (e.g., video decoder 30) can decode pictures in the viewwithout reference to pictures in any other view. When coding a picturein one of the non-base views, a video coder (such as video encoder 20 orvideo decoder 30) may add a picture into a reference picture list if thepicture is in a different view but within a same time instance (i.e.access unit) as the picture that the video coder is currently coding.Like other inter prediction reference pictures, the video coder mayinsert an inter-view prediction reference picture at any position of areference picture list.

Video coding standards specify video buffering models. In H.264/AVC andHEVC, a buffering model is referred to as a “hypothetical referencedecoder” or “HRD.” In HEVC Working Draft 8, the HRD is described inAnnex C.

The HRD describes how data is to be buffered for decoding and howdecoded data is buffered for output. For instance, the HRD describes theoperation of a coded picture buffer (“CPB”), a decoded picture buffer(“DPB”), and a video decoder. The CPB is a first-in first-out buffercontaining access units in a decoding order specified by HRD. The DPB isa buffer holding decoded pictures for reference, output reordering, oroutput delay specified by the HRD. The behaviors of the CPB and DPB maybe mathematically specified. The HRD may directly impose constraints ontiming, buffer sizes, and bit rates. Furthermore, the HRD may indirectlyimpose constraints on various bitstream characteristics and statistics.

In H.264/AVC and HEVC, bitstream conformance and decoder conformance arespecified as parts of the HRD specification. In other words, the HRDmodel specifies tests to determine whether a bitstream conforms to astandard and tests to determine whether a decoder conforms to thestandard. Though the HRD is named some kind of decoder, video encoderstypically use the HRD to guarantee bitstream conformance, while videodecoders typically do not need the HRD.

H.264/AVC and HEVC both specify two types of bitstream or HRDconformance, namely Type I and Type II. A Type I bitstream is a NAL unitstream containing only the VCL NAL units and filler data NAL unit forall access units in the bitstream. A Type II bitstream is a NAL unitstream that contains, in addition to the VCL NAL units and filler dataNAL units for all access units in the bitstream, at least one of thefollowing: additional non-VCL NAL units other than filler data NALunits; and all leading_zero_(—)8 bits, zero_byte,start_coded_prefix_one_(—)3 bytes, and trailing_zero_(—)8 bits syntaxelements that form a byte stream from the NAL unit stream.

When a device performs a bitstream conformance test that determineswhether a bitstream conforms to a video coding standard, the device mayselect an operation point of the bitstream. The device may thendetermine a set of HRD parameters applicable to the selected operationpoint. The device may use the set of HRD parameters applicable to theselected operation point to configure the behavior of the HRD. Moreparticularly, the device may use the applicable set of HRD parameters toconfigure the behaviors of particular components of the HRD, such as ahypothetical stream scheduler (HSS), the CPB, a decoding process, theDPB, and so on. Subsequently, the HSS may inject coded video data of thebitstream into the CPB of the HRD according to a particular schedule.

Furthermore, the device may invoke a decoding process that decodes thecoded video data in the CPB. The decoding process may output decodedpictures to the DPB. As the device moves data through the HRD, thedevice may determine whether a particular set of constraints remainsatisfied. For example, the device may determine whether an overflow orunderfiow condition occurs in the CPB or DPB while the HRD is decodingthe operation point representation of the selected operation point. Thedevice may select and process each operation point of the bitstream inthis manner. If no operation point of the bitstream causes theconstraints to be violated, the device may determine that the bitstreamconforms to the video coding standard.

Both H.264/AVC and HEVC specify two types of decoder conformance, namelyoutput timing decoder conformance and output order decoder conformance.A decoder claiming conformance to a specific profile, tier and level isable to successfully decode all bitstreams that conform to the bitstreamconformance requirements of a video coding standard, such as HEVC. Inthis disclosure, a “profile” may refer to a subset of the bitstreamsyntax. “Tiers” and “levels” may be specified within each profile. Alevel of a tier may be a specified set of constraints imposed on valuesof the syntax elements in the bitstream. These constraints may be simplelimits on values. Alternatively, they may take the form of constraintson arithmetic combinations of values (e.g., picture width multiplied bypicture height multiplied by number of pictures decoded per second). Alevel specified for a lower tier is more constrained than a levelspecified for a higher tier.

When a device performs a decoder conformance test to determine whether adecoder under test (DUT) conforms to a video coding standard, the devicemay provide to both the HRD and the DUT a bitstream that conforms to thevideo coding standard. The HRD may process the bitstream in the mannerdescribed above with regard to the bitstream conformance test. Thedevice may determine that the DUT conforms to the video coding standardif the order of decoded pictures output by the DUT matches the order ofdecoded pictures output by the HRD. Moreover, the device may determinethat the DUT conforms to the video coding standard if the timing withwhich the DUT outputs decoded pictures matches the timing with which theHRD outputs the decoded pictures.

In addition to bitstream conformance tests and decoder conformancetests, devices may use HRD parameters for other purposes. For examples,the initial CPB removal delays may be used to guide a system to set upan appropriate initial end-to-end delay and the DPB output times may beused to derive real-time protocol (RTP) timestamps when the video databitstream is transported over RTP.

In the H.264/AVC and HEVC HRD models, decoding or CPB removal may beaccess unit based. That is, the HRD is assumed to decode complete accessunits at one time and remove complete access units from the CPB.Furthermore, in the H.264/AVC and HEVC HRD models, it is assumed thatpicture decoding is instantaneous. Video encoder 20 may signal, inpicture timing SEI messages, decoding times to start decoding of accessunits. In practical applications, if a conforming video decoder strictlyfollows the decoding times signaled to start decoding of access units,the earliest possible time to output a particular decoded picture isequal to the decoding time of that particular picture plus the timeneeded for decoding that particular picture. However, in the real-world,the time needed for decoding a picture cannot be equal to zero.

HRD parameters may control various aspects of the HRD. In other words,the HRD may rely on the HRD parameters. The HRD parameters may includean initial CPB removal delay, a CPB size, a bit rate, an initial DPBoutput delay, and a DPB size. Video encoder 20 may signal these HRDparameters in a hrd_parameters( ) syntax structure specified in a videoparameter set (VPS) and/or a sequence parameter set (SPS). IndividualVPS's and/or SPS's may include multiple hrd_parameters( ) syntaxstructures for different sets of HRD parameters. In some examples, videoencoder 20 may signal HRD parameters in buffering period SEI messages orpicture timing SEI messages.

As explained above, an operation point of a bitstream is associated witha set of layer identifiers (i.e., a set of nuh_reserved_zero_(—)6 bitsvalues) and a temporal identifier. An operation point representation mayinclude each NAL unit that is associated with the operation point. Anoperation point representation may have a different frame rate and/orbit rate than an original bitstream. This is because the operation pointrepresentation may not include some pictures and/or some of the data ofthe original bitstream. Hence, if video decoder 30 were to remove datafrom the CPB and/or the DPB at a particular rate when processing theoriginal bitstream and if video decoder 30 were to remove data from theCPB and/or the DPB at the same rate when processing an operation pointrepresentation, video decoder 30 may remove too much or too little datafrom the CPB and/or the DPB. Accordingly, video encoder 20 may signaldifferent sets of HRD parameters for different operation points. Forinstance, video encoder 20 may include, in a VPS, multiplehrd_parameters( ) syntax structures that include HRD parameters fordifferent operation points.

In HEVC Working Draft 8, the set of HRD parameters optionally includes aset of information that is common for all sub-layers. In other words,the set of HRD parameters may optionally include a set of common syntaxelements that are applicable to operation points that include anytemporal sub-layers. A temporal sub-layer is a temporal scalable layerof a temporal scalable bitstream consisting of VCL NAL units with aparticular value of TemporalId and the associated non-VCL NAL units. Inaddition to the set of common information, the sets of HRD parametersmay include a set of syntax elements that are specific to individualtemporal sub-layers. For instance, the hrd_parameters( ) syntaxstructure may optionally include a set of information that is common forall sub-layers and always includes sub-layer-specific information.Because the set of common information is common to multiple sets of HRDparameters, it may be unnecessary to signal the set of commoninformation in multiple sets of HRD parameters. Rather, in HEVC WorkingDraft 8, the common information may be present in a set of HRDparameters when the set of HRD parameters is the first set of HRDparameters in a VPS or the common information may be present in a set ofHRD parameters when the set of HRD parameters is associated with thefirst operation point index. For instance, HEVC Working Draft 8 supportsthe presence of common information when either the hrd_parameters( )syntax structure is the first hrd_parameters( ) syntax structure in theVPS or when the hrd_parameters( ) syntax structure is associated with afirst operation point.

Table 1, below, is an example syntax structure for a hrd_parameters( )syntax structure in HEVC.

TABLE 1 HRD Parameters hrd_parameters( commonInfPresentFlag,MaxNumSubLayersMinus1 ) { Descriptor  if( commonInfPresentFlag ) {  timing_info_present_flag u(1)   if( timing_info_present_flag ) {   num_units_in_tick u(32)    time_scale u(32)   }  nal_hrd_parameters_present_flag u(1)   vcl_hrd_parameters_present_flagu(1)   if( nal_hrd_parameters_present_flag ||  vcl_hrd_parameters_present_flag ){    sub_pic_cpb_params_present_flagu(1)    if( sub_pic_cpb_params_present_flag ) {     tick_divisor_minus2u(8)     du_cpb_removal_delay_length_minus1 u(5)    }    bit_rate_scaleu(4)    cpb_size_scale u(4)    initial_cpb_removal_delay_length_minus1u(5)    cpb_removal_delay_length_minus1 u(5)   dpb_output_delay_length_minus1 u(5)   }  }  for( i = 0; i <=MaxNumSubLayersMinus1; i++ ) {   fixed_pic_rate_flag[ i ] u(1)   if(fixed_pic_rate_flag[ i ] )    pic_duration_in_tc_minus1[ i ] ue(v)  low_delay_hrd_flag[ i ] u(1)   cpb_cnt_minus1[ i ] ue(v)   if(nal_hrd_parameters_present_flag )    sub_layer_hrd_parameters( i )   if(vcl_hrd_parameters_present_flag )    sub_layer_hrd_parameters( i )  } }

In the example of Table 1, above, and other syntax tables of thisdisclosure, syntax elements with type descriptor ue(v) may bevariable-length unsigned integers encoded using 0^(th) order exponentialGolomb (Exp-Golomb) coding with left bit first. In the example of Table1 and the following tables, syntax elements having descriptors of theform u(n), where n is a non-negative integer, are unsigned values oflength n.

In the example syntax of Table 1, the syntax elements in the “if(commonInfPresentFlag) { . . . }” block are the common information ofthe HRD parameter sets. In other words, the common information of set ofHRD parameters may include the syntax elements timing_info_present_flag,num_units_in_tick, time_scale, nal_hrd_parameters_present_flag,vcl_hrd_parameters_present_flag, sub_pic_cpb_params_present_flag,tick_divisor_minus2, du_cpb_removal_delay_length_minus1, bit_rate_scale,cpb_size_scale, initial_cpb_removal_delay_length_minus1,cpb_removal_delay_length_minus1, and dpb_output_delay_length_minus1.

Furthermore, in the example of Table 1, the syntax elementsfixed_pic_rate_flag[i], pic_duration_in_tc_minus1[i],low_delay_hrd_flag[i], and cpb_cnt_minus1[i] may be a set ofsub-layer-specific HRD parameters. In other words, these syntax elementof the hrd_parameters( ) syntax structure may only be applicable tooperation points that include a specific sub-layer. Thus, the HRDparameters of a hrd_parameters( ) syntax structure may include, inaddition to the optionally-included common information, a set ofsub-layer-specific HRD parameters that is specific to a particularsub-layer of the bitstream.

The fixed_pic_rate_flag[i] syntax element may indicate that, whenHighestTid is equal to i, the temporal distance between the HRD outputtimes of any two consecutive pictures in output order is constrained aspecific way. HighestTid may be a variable that identifies a highesttemporal sub-layer (e.g., of an operation point). Thepic_duration_in_tc_minus1[i] syntax element may specify, when HighestTidis equal to i, the temporal distance, in clock ticks, between the HRDoutput times of any consecutive pictures in output order in the codedvideo sequence. The low_delay_hrd_flag[i] syntax element may specify theHRD operation mode, when HighestTid is equal to i, as specified in AnnexC of HEVC Working Draft 8. The cpb_cnt_minus1[i] syntax element mayspecify the number of alternative CPB specifications in the bitstream ofthe coded video sequence when HighestTid is equal to i.

Video encoder 20 may use SEI messages to include, in the bitstream,metadata that is not required for correct decoding of the sample valuesof pictures. However, video decoder 30 or other devices may use themetadata included in SEI messages for various other purposes. Forexample, video decoder 30 may use the metadata in SEI messages forpicture output timing, picture displaying, loss detection, and errorconcealment.

Video encoder 20 may include one or more SEI NAL units in an accessunit. In other words, any number of SEI NAL units may be associated withan access unit. Furthermore, each SEI NAL unit may contain one or moreSEI messages. The HEVC standard describes the syntax and semantics forvarious types of SEI messages. However, the HEVC standard does notdescribe the handling of the SEI messages because the SEI messages donot affect the normative decoding process. One reason to have SEImessages in the HEVC standard is to enable supplemental data beinginterpreted identically in different systems using HEVC. Specificationsand systems using HEVC may require video encoders to generate certainSEI messages or may define specific handling of particular types ofreceived SEI messages. Table 2, below, lists SEI messages specified inHEVC and briefly describes their purposes.

TABLE 2 Overview of SEI messages SEI message Purpose Buffering periodInitial delays for hypothetical reference decoder (HRD) operationPicture timing Picture output time and picture/sub-picture removal timefor HRD operation Pan-scan rectangle Displaying at a different pictureaspect ratio (PAR) than the PAR of the output pictures Filler payloadAdjusting the bitrate to meet specific constraints User data registeredSEI messages to be specified by external entities User data unregisteredRecovery point Additional information for clean random access. Gradualdecoding refresh. Scene information Information about scene changes andtransitions Full-frame snapshot Indication to label the associateddecoded picture as a still- image snapshot of the video contentProgressive Indicates that certain consecutive pictures represent arefinement segment progressive refinement of the quality of a picturerather than a moving scene Film grain Enables decoders to synthesizefilm grain characteristics Deblocking filter Recommends whether or notdisplayed pictures should display preference undergo the in-loopdeblocking filter process Post-filter hint Provides suggestedpost-filter coefficients or correlation information for post-filterdesign Tone mapping Remapping to another color space than that used orassumed information in encoding Frame packing Packing of stereoscopicvideo into an HEVC bitstream arrangement Display orientation Specifiesflipping and/or rotation that should be applied to the output pictureswhen they are displayed Field indication Provides information related tointerlaced video content and/or field coding, e.g. indicates whether thepicture is a progressive frame, a field, or a frame containing twointerleaved fields Decoded picture hash Checksum of the decoded picture,which may be used for error detection Sub-picture timing Sub-pictureremoval time for HRD operation Active parameter sets Providesinformation on active VPS, SPS, etc. Structure of Pictures Describes thetemporal and inter prediction structure of the description bitstream

There are several problems or shortcomings with existing techniques forsignaling HRD parameters and selection of HRD parameters and otherparameters. For example, in HEVC Working Draft 8, only the sets of HRDparameters in the VPS are selected for HRD operations. That is, althoughHRD parameters can be provided in SPS's, the sets of HRD parameters inSPS's are not selected by HEVC video decoders for HRD operations. Videodecoders always parse and decode the VPS of a bitstream. Hence, videodecoders always parse and decode the sets of HRD parameters of the VPS.

This is true regardless of whether the bitstream includes non-base layerNAL units. For instance, only the hrd_parameters( ) syntax structurecoded in the VPS may be selected for HRD operations, and thepossibly-present hrd_parameters( ) syntax structure in the SPS may neverbe selected. This may require the parsing and handling of the VPS, evenwhen decoding a bitstream that does not contain nuh_reserved_zero_(—)6bits greater than 0 (i.e., the bitstream contains only the base layer ina multiview, 3DV, or SVC extension of HEVC).

Thus, if the bitstream includes non-base layer NAL units, it may be awaste of computational resources to parse and handle the sets of HRDparameters in the SPS's. Furthermore, if the sets of HRD parameters arepresent in the VPS, the sets of HRD parameters in the SPS's may bewasted bits. For instance, if an hrd_parameters( ) syntax structure ispresent in the SPS, the coded bits for the syntax structure may bepurely a waste of bits.

In accordance with one or more techniques of this disclosure, videoencoder 20 may generate a bitstream that includes an SPS that isapplicable to a sequence of pictures. The SPS includes a set of HRDparameters. The set of HRD parameters is applicable to each operationpoint of the bitstream that has a set of layer identifiers that matchesa set of target layer identifiers. Thus, the sets of HRD parameters inthe SPS's are not wasted, but rather may be used for HRD operations. Forinstance, the operation points to which the hrd_parameters( ) syntaxstructure coded in a SPS may be clearly specified, e.g. to be theoperation points for which only one value of nuh_reserved_zero_(—)6 bits(i.e., layer ID in a multiview, 3DV or scalable video coding extension)is present in the bitstream.

For example, a device, such as video encoder 20 or video decoder 30, mayselect, from among a set of HRD parameters in a video parameter set anda set of HRD parameters in a SPS, a set of HRD parameters applicable toa particular operation point. In this example, the device may perform,based at least in part on the set of HRD parameters applicable to theparticular operation point, a bitstream conformance test that testswhether a bitstream subset associated with the particular operationpoint conforms to a video coding standard. The bitstream conformancetest may verify that the operation point representation conforms to avideo coding standard, such as HEVC.

In this disclosure, an operation point may be identified by a set ofnuh_reserved_zero_(—)6 bits values, denoted as OpLayerIdSet, and aTemporalId value, denoted as OpTid. The associated bitstream subsetderived as the output of the sub-bitstream extraction process asspecified in subclause 10.1 of HEVC Working Draft 8 with OpTid andOpLayerIdSet as inputs is independently decodable. Subclause 10.1 ofHEVC Working Draft 8 describes an operation for extracting asub-bitstream (i.e., an operation point representation) from thebitstream. Specifically, subclause 10.1 of HEVC Working Draft 8 providesthat the sub-bitstream is derived by removing from the bitstream all NALunits with temporal identifiers (e.g., TemporalID) greater thantIdTarget or layer identifiers (e.g., nuh_reserved_zero_(—)6 bits) notamong the values in targetDecLayerIdSet. tIdTarget andtargetDecLayerIdSet are parameters of the bitstream extraction process.

In another example problem or shortcoming with the existing techniquesfor signaling HRD parameters, a device, such as a video encoder, a videodecoder, or another type of device, may perform a bitstream conformancetest on an operation point representation for an operation point. Asmentioned above, a set of target layer identifiers and a temporalidentifier may be used to identify the operation point. The set oftarget layer identifiers may be denoted as “TargetDecLayerIdSet.” Thetemporal identifier may be denoted as “TargetDecHighestTid.”Problematically, HEVC Working Draft 8 does not specify howTargetDecLayerIdSet or TargetDecHighestTid are set when performing abitstream conformance test. For instance, when the decoding process isinvoked for a bitstream conformance test, the semantics of syntaxelements are not clearly specified as the values of TargetDecLayerIdSetand TargetDecHighestTid are not properly set.

One or more techniques of this disclosure indicate howTargetDecLayerIdSet and TargetDecHighestTid are set when performing abitstream conformance test. For instance, the general decoding processfor a bitstream (or operation point representation) is modified suchthat if the bitstream (or operation point representation) is decoded ina bitstream conformance test, TargetDecLayerIdSet is set as specified insubclause C.1 of the HEVC standard. Similarly, the general decodingprocess for a bitstream (or operation point representation) may bemodified such that if the bitstream (or operation point representation)is decoded in a bitstream conformance test, TargetDecHighestTid is setas specified in subclause C.1 of HEVC Working Draft 8. In other words,the device may determine a target layer identifier set of the particularoperation point that contains each layer identifier present in thebitstream subset and the layer identifier set of the particularoperation point is a subset of layer identifiers present in thebitstream. In addition, the device may determine a target temporalidentifier of the particular operation point that is equal to a greatesttemporal identifier present in the bitstream subset and the targettemporal identifier of the particular operation point is less than orequal to the greatest temporal identifier present in the bitstream.

In subclause C.1 of HEVC Working Draft 8, TargetDecLayerIdSet is set totargetOpLayerIdSet. targetOpLayerIdSet contains the set of values fornuh_reserved_zero_(—)6 bits present in the operation pointrepresentation of the operation point under test. targetOpLayerIdSet isa subset of the values for nuh_reserved_zero_(—)6 bits present in thebitstream under test.

Furthermore, the variable TargetDecHighestTid identifies the highesttemporal sub-layer to be decoded. A temporal sub-layer is a temporalscalable layer of a temporal scalable bitstream consisting of VCL NALunits with a particular value of TemporalId and the associated non-VCLNAL units. In subclause C.1 of the HEVC standard, TargetDecHighestTid isset to targetOpTid. targetOpTid is equal to the greatest temporal_idpresent in the operation point representation of the operation pointunder test and is less than or equal to the greatest temporal_id presentin the bitstream under test. Thus, when the decoding process is invokedfor a bitstream conformance test, the values of TargetDecLayerIdSet andTargetDecHighestTid are set to the set of nuh_reserved_zero_(—)6 bitsvalues and the greatest TemporalId value present in the sub-bitstreamcorresponding to the operation point under test for the specificbitstream conformance test.

In this way, a device (such as video encoder 20, video decoder 30,additional device 21, or another device) may, in accordance with one ormore techniques of this disclosure, perform a decoding process as partof performing a bitstream conformance test. Performing the decodingprocess may comprise performing a bitstream extraction process toextract, from a bitstream, an operation point representation of anoperation point defined by a target set of layer identifiers and atarget highest temporal identifier. The target set of layer identifiers(i.e., TargetDecLayerIdSet) contains values of layer identifier syntaxelements (e.g., nuh_reserved_zero_(—)6 bits syntax elements) present inthe operation point representation. The target set of layer identifiersis a subset of values of layer identifier syntax elements of thebitstream. The target highest temporal identifier (i.e.,TargetDecHighestTid) is equal to a greatest temporal identifier presentin the operation point representation. The target highest temporalidentifier is less than or equal to a greatest temporal identifierpresent in the bitstream. Performing the decoding process also comprisesdecoding NAL units of the operation point representation.

The decoding process is not always performed as part of performing abitstream conformance test. Rather, the decoding process may be ageneral process for decoding a bitstream. When the decoding process isnot performed as part of a bitstream conformance test, an externalsource may specify TargetDecLayerIdSet and TargetDecHighestTid for anoperation point. The external source may be any source of informationoutside the bitstream. For example, a CDN device may programmaticallydetermine and specify TargetDecLayerIdSet and TargetDecHighestTid basedon the configuration of a particular video decoder. The deviceperforming the decoding process may use the externally-specifiedTargetDecLayerIdSet and TargetDecHighestTid to extract the operationpoint representation from the bitstream. The device performing thedecoding process may then decode NAL units of the extracted operationpoint representation.

Thus, when the decoding process is not performed as part of thebitstream conformance test, the device performing the decoding processmay receive, from an external source, a target set of layer identifiersand a target highest temporal identifier. The target set of layeridentifiers contains values of layer identifier syntax elements presentin an operation point representation. The target highest temporalidentifier is equal to a greatest temporal identifier present in thesecond operation point representation. Furthermore, the deviceperforming the decoding process may perform the bitstream extractionprocess to extract, from the bitstream, the operation pointrepresentation. The device performing the decoding process may thendecode NAL units of the operation point representation.

In other instances, an external source does not specifyTargetDecLayerIdSet or TargetDecHighestTid. In such instances, thedecoding process may be performed on the whole bitstream. For example,the device may perform the bitstream extraction process to extract, fromthe bitstream, an operation point representation. In this example, 0 isthe only value of layer identifier syntax elements (i.e.,nuh_reserved_zero_(—)6 bits) present in the operation pointrepresentation. Furthermore, in this example, the greatest temporalidentifier present in the bitstream is equal to a greatest temporalidentifier present in the operation point representation. In thisexample, the device performing the decoding process may decode NAL unitsof the operation point representation.

As indicated above, a SPS may include an array of syntax elementsdenoted as sps_max_dec_pic_buffering[i], where i ranges from 0 to themaximum number of temporal layers in the bitstream.sps_max_dec_pic_buffering[i] indicates the maximum required size of theDPB when a highest temporal identifier (HighestTid) is equal to i.sps_max_dec_pic_buffering[i] indicates the required size in terms ofunits of picture storage buffers. Furthermore, a SPS may include anarray of syntax elements denoted by sps_max_num_reorder_pics[i], where iranges from 0 to the maximum number of temporal layers in the bitstream.sps_max_num_reorder_pics[i] indicates a maximum allowed number ofpictures preceding any picture in decoding order and succeeding thatpicture in output order when a highest temporal identifier (HighestTid)is equal to i. In addition, a set of HRD parameters may include an arrayof syntax elements denoted cpb_cnt_minus1[i], where i ranges from 0 tothe maximum number of temporal layers in the bitstream.cpb_cnt_minus1[i] specifies the number of alternative CPB specificationsin the bitstream of the coded video sequence when a highest temporalidentifier (HighestTid) is equal to i.

Because HEVC Working Draft 8 does not specify what is meant by thehighest temporal identifier (HighestTid), HEVC Working Draft 8,sps_max_dec_pic_buffering[i], sps_max_num_reorder_pics[i], andcpb_cnt_minus1[i] are not properly selected in HRD operations, bitstreamconformance operations, and level restrictions. In other words, theparameters sps_max_num_reorder_pics[i], sps_max_dec_pic_buffering[i],and cpb_cnt_minus1[i] in the HRD operations, bitstream conformancerequirements and level restrictions are not properly selected.

In accordance with one or more techniques of this disclosure,sps_max_dec_pic_buffering[i] is defined such thatsps_max_dec_pic_buffering[i] indicates the maximum required size of theDPB when TargetDecHighestTid is equal to i. TargetDecHighestTid isdetermined in the manner described above. This may stand in contrast toHEVC Working Draft 8, where HighestTid is not defined. The value ofsps_max_dec_pic_buffering[i] shall be in the range of 0 to MaxDpbSize(as specified in subclause A.4 of HEVC Working Draft 8), inclusive. Wheni is greater than 0, sps_max_dec_pic_buffering[i] shall be equal to orgreater than sps_max_dec_pic_buffering[i−1]. The value ofsps_max_dec_pic_buffering[i] shall be less than or equal tovps_max_dec_pic_buffering[i] for each value of i.

Similarly, in accordance with one or more techniques of this disclosure,sps_max_num_reorder_pics[i] is defined such thatsps_max_num_reorder_pics[i] indicates the maximum allowed number ofpictures preceding any picture in decoding order and succeeding thatpicture in output order when TargetDecHighestTid is equal to i.TargetDecHighestTid is determined in the manner described above. Thevalue of sps_max_num_reorder_pics[i] shall be in the range of 0 tosps_max_dec_pic_buffering[i], inclusive. When i is greater than 0,sps_max_num_reorder_pics[i] shall be equal to or greater thansps_max_num_reorder_pics[i−1]. The value of sps_max_num_reorder_pics[i]shall be less than or equal to vps_max_num_reorder_pics[i] for eachvalue of i.

Furthermore, in accordance with one or more techniques of thisdisclosure, cpb_cnt_minus1[i] may specify the number of alternative CPBspecifications in the bitstream of the coded video sequence whenTargetDecHighestTid is equal to i, where i ranges from 0 to the maximumnumber of temporal layers in the bitstream. TargetDecHighestTid isdetermined in the manner described above. The value of cpb_cnt_minus1[i]is in the range of 0 to 31, inclusive. When low_delay_hrd_flag[i] isequal to 1, cpb_cnt_minus1[i] is equal to 0. When cpb_cnt_minus1[i] isnot present, cpb_cnt_minus1[i] is inferred to be equal to 0.

Thus, in accordance with one or more techniques of this disclosure, adevice may determine, based on a highest temporal identifier, aparticular syntax element from among an array of syntax elements. Thehighest temporal identifier is defined such that the highest temporalidentifier always identifies a highest temporal layer to be decoded.Thus, sps_max_num_reorder_pics[i], sps_max_dec_pic_buffering[i], andcpb_cnt_minus1[i] in the HRD operations, bitstream conformancerequirements and level restrictions are consistently selected with iequal to the clearly specified value of TargetDecHighestTid.

In this way, a device (such a video encoder 20, video decoder 30,additional device 21, or another device) may perform a HRD operation todetermine conformance of a bitstream to a video coding standard or todetermine conformance of a video decoder to the video coding standard.As part of performing the HRD operation, the device may determine ahighest temporal identifier of a bitstream-subset associated with aselected operation point of the bitstream. In addition, the device maydetermine, based on the highest temporal identifier, a particular syntaxelement from among an array of syntax elements (e.g.,sps_max_num_reorder_pics[i], sps_max_dec_pic_buffering[i], orcpb_cnt_minus1[i]). Furthermore, the device may use the particularsyntax element in the HRD operation.

Furthermore, in HEVC Working Draft 8, each of the hrd_parameters( )syntax structures in the VPS may be associated with anoperation_point_layer_ids( ) syntax structure based on which ahrd_parameters( ) syntax structure is selected for use in the HRDoperations. Corresponding to each selected hrd_parameters( ) syntaxstructure, a set of buffering period SEI messages and picture timing SEImessages may also be needed in the HRD operations. However, there is noway to associate a buffering period SEI message or picture timing SEImessage to a hrd_parameters( ) syntax structure for which the associatedoperation_point_layer_ids( ) syntax structure includes multiple valuesof nuh_reserved_zero_(—)6 bits (i.e., multiple layer IDs in a multiview,3DV or scalable video coding extension of HEVC).

A solution to this problem may be to apply the multi-view codingscalable nesting SEI message as specified in Annex H of H.264/AVC orsimilar. However, the multi-view coding scalable nesting SEI message orsimilar SEI messages may have the following disadvantages. Firstly,since SEI NAL units in H.264/AVC only have a one-byte NAL unit header,there may be no way to use the information carried innuh_reserved_zero_(—)6 bits and temporal_id_plus1 in the NAL unit headerof the HEVC SEI NAL unit for association of a buffering period orpicture timing SEI message to operation points. Secondly, each nestedSEI message can only be associated with one operation point.

One or more techniques of this disclosure may provide a mechanism toclearly specify the operation points to which a buffering period SEImessage, picture timing SEI message or sub-picture timing SEI messageapplies, through the applicable_operation_points( ) syntax structurethat may be carried in a buffering period SEI message, picture timingSEI message, or sub-picture timing SEI message. The mechanism may allowuse the information carried in the syntax elementsnuh_reserved_zero_(—)6 bits and temporal_id_plus1 in the NAL unit headerof SEI NAL units, and may allow the sharing of the information conveyedin a same buffering period, picture timing or sub-picture timing SEImessage by multiple operation points.

FIG. 2 is a block diagram illustrating an example video encoder 20 thatmay implement the techniques of this disclosure. FIG. 2 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 20 inthe context of HEVC coding. However, the techniques of this disclosuremay be applicable to other coding standards or methods.

In the example of FIG. 2, video encoder 20 includes a predictionprocessing unit 100, a residual generation unit 102, a transformprocessing unit 104, a quantization unit 106, an inverse quantizationunit 108, an inverse transform processing unit 110, a reconstructionunit 112, a filter unit 114, a decoded picture buffer 116, and anentropy encoding unit 118. Prediction processing unit 100 includes aninter-prediction processing unit 120 and an intra-prediction processingunit 126. Inter-prediction processing unit 120 includes a motionestimation unit 122 and a motion compensation unit 124. In otherexamples, video encoder 20 may include more, fewer, or differentfunctional components.

Video encoder 20 may receive video data. Video encoder 20 may encodeeach CTU in a slice of a picture of the video data. Each of the CTUs maybe associated with equally-sized luma coding tree blocks (CTBs) andcorresponding CTBs of the picture. As part of encoding a CTU, predictionprocessing unit 100 may perform quad-tree partitioning to divide theCTBs of the CTU into progressively-smaller blocks. The smaller block maybe coding blocks of CUs. For example, prediction processing unit 100 maypartition a CTB associated with a CTU into four equally-sizedsub-blocks, partition one or more of the sub-blocks into fourequally-sized sub-sub-blocks, and so on.

Video encoder 20 may encode CUs of a CTU to generate encodedrepresentations of the CUs (i.e., coded CUs). As part of encoding a CU,prediction processing unit 100 may partition the coding blocksassociated with the CU among one or more PUs of the CU. Thus, each PUmay be associated with a luma prediction block and corresponding chromaprediction blocks. Video encoder 20 and video decoder 30 may support PUshaving various sizes. The size of a CU may refer to the size of the lumacoding block of the CU and the size of a PU may refer to the size of aluma prediction block of the PU. Assuming that the size of a particularCU is 2N×2N, video encoder 20 and video decoder 30 may support PU sizesof 2N×2N or N×N for intra prediction, and symmetric PU sizes of 2N×2N,2N×N, N×2N, N×N, or similar for inter prediction. Video encoder 20 andvideo decoder 30 may also support asymmetric partitioning for PU sizesof 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

Inter-prediction processing unit 120 may generate predictive data for aPU by performing inter prediction on each PU of a CU. The predictivedata for the PU may include a predictive blocks of the PU and motioninformation for the PU. Inter-prediction processing unit 12 may performdifferent operations for a PU of a CU depending on whether the PU is inan I slice, a P slice, or a B slice. In an I slice, all PUs are intrapredicted. Hence, if the PU is in an I slice, inter-predictionprocessing unit 120 does not perform inter prediction on the PU. Thus,for blocks encoded in I-mode, the predictive block is formed usingspatial prediction from previously-encoded neighboring blocks within thesame frame.

If a PU is in a P slice, motion estimation unit 122 may search thereference pictures in a list of reference pictures (e.g., “RefPicList0”)for a reference region for the PU. The reference region for the PU maybe a region, within a reference picture, that contains sample blocksthat most closely correspond to the prediction blocks of the PU. Motionestimation unit 122 may generate a reference index that indicates aposition in RefPicList0 of the reference picture containing thereference region for the PU. In addition, motion estimation unit 122 maygenerate a motion vector that indicates a spatial displacement between aprediction block of the PU and a reference location associated with thereference region. For instance, the motion vector may be atwo-dimensional vector that provides an offset from the coordinates inthe current picture to coordinates in a reference picture. Motionestimation unit 122 may output the reference index and the motion vectoras the motion information of the PU. Motion compensation unit 124 maygenerate the predictive blocks of the PU based on actual or interpolatedsamples at the reference location indicated by the motion vector of thePU.

If a PU is in a B slice, motion estimation unit 122 may performuni-prediction or bi-prediction for the PU. To perform uni-predictionfor the PU, motion estimation unit 122 may search the reference picturesof RefPicList0 or a second reference picture list (“RefPicList1”) for areference region for the PU. Motion estimation unit 122 may output, asthe motion information of the PU, a reference index that indicates aposition in RefPicList0 or RefPicList1 of the reference picture thatcontains the reference region, a motion vector that indicates a spatialdisplacement between a sample block of the PU and a reference locationassociated with the reference region, and one or more predictiondirection indicators that indicate whether the reference picture is inRefPicList0 or RefPicList1. Motion compensation unit 124 may generatethe predictive blocks of the PU based at least in part on actual orinterpolated samples at the reference region indicated by the motionvector of the PU.

To perform bi-directional inter prediction for a PU, motion estimationunit 122 may search the reference pictures in RefPicList0 for areference region for the PU and may also search the reference picturesin RefPicList1 for another reference region for the PU. Motionestimation unit 122 may generate reference indexes that indicatepositions in RefPicList0 and RefPicList1 of the reference pictures thatcontain the reference regions. In addition, motion estimation unit 122may generate motion vectors that indicate spatial displacements betweenthe reference location associated with the reference regions and asample block of the PU. The motion information of the PU may include thereference indexes and the motion vectors of the PU. Motion compensationunit 124 may generate the predictive blocks of the PU based at least inpart on actual or interpolated samples at the reference region indicatedby the motion vector of the PU.

Intra-prediction processing unit 126 may generate predictive data for aPU by performing intra prediction on the PU. The predictive data for thePU may include predictive blocks for the PU and various syntax elements.Intra-prediction processing unit 126 may perform intra prediction on PUsin I slices, P slices, and B slices.

To perform intra prediction on a PU, intra-prediction processing unit126 may use multiple intra prediction modes to generate multiple sets ofpredictive data for the PU. To use an intra prediction mode to generatea set of predictive data for the PU, intra-prediction processing unit126 may extend samples from sample blocks of neighboring PUs across thesample blocks of the PU in a direction associated with the intraprediction mode. The neighboring PUs may be above, above and to theright, above and to the left, or to the left of the PU, assuming aleft-to-right, top-to-bottom encoding order for PUs, CUs, and CTUs.Intra-prediction processing unit 126 may use various numbers of intraprediction modes, e.g., 33 directional intra prediction modes. In someexamples, the number of intra prediction modes may depend on the size ofthe region associated with the PU.

Prediction processing unit 100 may select the predictive data for PUs ofa CU from among the predictive data generated by inter-predictionprocessing unit 120 for the PUs or the predictive data generated byintra-prediction processing unit 126 for the PUs. In some examples,prediction processing unit 100 selects the predictive data for the PUsof the CU based on rate/distortion metrics of the sets of predictivedata. The predictive blocks of the selected predictive data may bereferred to herein as the selected predictive blocks.

Residual generation unit 102 may generate, based on the luma, Cb and Crcoding block of a CU and the selected predictive luma, Cb and Cr blocksof the PUs of the CU, a luma, Cb and Cr residual blocks of the CU. Forinstance, residual generation unit 102 may generate the residual blocksof the CU such that each sample in the residual blocks has a value equalto a difference between a sample in a coding block of the CU and acorresponding sample in a corresponding selected predictive block of aPU of the CU.

Transform processing unit 104 may perform quad-tree partitioning topartition the residual blocks associated with a CU into transform blocksassociated with TUs of the CU. Thus, a TU may be associated with a lumatransform block and two chroma transform blocks. The sizes and positionsof the luma and chroma transform blocks of TUs of a CU may or may not bebased on the sizes and positions of prediction blocks of the PUs of theCU. A quad-tree structure known as a “residual quad-tree” (RQT) mayinclude nodes associated with each of the regions. The TUs of a CU maycorrespond to leaf nodes of the RQT.

Transform processing unit 104 may generate transform coefficient blocksfor each TU of a CU by applying one or more transforms to the transformblocks of the TU. Transform processing unit 104 may apply varioustransforms to a transform block associated with a TU. For example,transform processing unit 104 may apply a discrete cosine transform(DCT), a directional transform, or a conceptually similar transform to atransform block. In some examples, transform processing unit 104 doesnot apply transforms to a transform block. In such examples, thetransform block may be treated as a transform coefficient block.

Quantization unit 106 may quantize the transform coefficients in acoefficient block. The quantization process may reduce the bit depthassociated with some or all of the transform coefficients. For example,an n-bit transform coefficient may be rounded down to an m-bit transformcoefficient during quantization, where n is greater than m. Quantizationunit 106 may quantize a coefficient block associated with a TU of a CUbased on a quantization parameter (QP) value associated with the CU.Video encoder 20 may adjust the degree of quantization applied to thecoefficient blocks associated with a CU by adjusting the QP valueassociated with the CU. Quantization may introduce loss of information,thus quantized transform coefficients may have lower precision than theoriginal ones.

Inverse quantization unit 108 and inverse transform processing unit 110may apply inverse quantization and inverse transforms to a coefficientblock, respectively, to reconstruct a residual block from thecoefficient block. Reconstruction unit 112 may add the reconstructedresidual block to corresponding samples from one or more predictiveblocks generated by prediction processing unit 100 to produce areconstructed transform block associated with a TU. By reconstructingtransform blocks for each TU of a CU in this way, video encoder 20 mayreconstruct the coding blocks of the CU.

Filter unit 114 may perform one or more deblocking operations to reduceblocking artifacts in the coding blocks associated with a CU. Decodedpicture buffer 116 may store the reconstructed coding blocks afterfilter unit 114 performs the one or more deblocking operations on thereconstructed coding blocks. Inter-prediction unit 120 may use areference picture that contains the reconstructed coding blocks toperform inter prediction on PUs of other pictures. In addition,intra-prediction processing unit 126 may use reconstructed coding blocksin decoded picture buffer 116 to perform intra prediction on other PUsin the same picture as the CU.

Entropy encoding unit 118 may receive data from other functionalcomponents of video encoder 20. For example, entropy encoding unit 118may receive coefficient blocks from quantization unit 106 and mayreceive syntax elements from prediction processing unit 100. Entropyencoding unit 118 may perform one or more entropy encoding operations onthe data to generate entropy-encoded data. For example, entropy encodingunit 118 may perform a context-adaptive variable length coding (CAVLC)operation, a CABAC operation, a variable-to-variable (V2V) length codingoperation, a syntax-based context-adaptive binary arithmetic coding(SBAC) operation, a Probability Interval Partitioning Entropy (PIPE)coding operation, an Exponential-Golomb encoding operation, or anothertype of entropy encoding operation on the data. Video encoder 20 mayoutput a bitstream that includes entropy-encoded data generated byentropy encoding unit 118. For instance, the bitstream may include datathat represents a RQT for a CU.

As indicated elsewhere in this disclosure, video encoder 20 may signal aVPS in the bitstream. In HEVC Working Draft 8, particular syntaxelements of the VPS vps_max_dec_pic_buffering[i],vps_max_num_reorder_pics[i], and vps_max_latency_increase[i]) aredefined with reference to a value HighestTid, which is not defined. Inaccordance with one or more techniques of this disclosure, these syntaxelements of the VPS may be defined with reference to a valueTargetDecHighestTid, which is defined such that the TargetDecHighestTidas described elsewhere in this disclosure. Table 3, below, illustrates asyntax of a VPS in accordance with one or more techniques of thisdisclosure.

TABLE 3 VPS De- video_parameter_set_rbsp( ) { scriptor video_parameter_set_id u(4)  vps_temporal_id_nesting_flag u(1) vps_reserved_zero_2bits u(2)  vps_reserved_zero_6bits u(6) vps_max_sub_layers_minus1 u(3)  profile_tier_level( 1,vps_max_sub_layers_minus1 )  vps_reserved_zero_12bits u(12)  for( i = 0;i <= vps_max_sub_layers_minus1; i++ ) {   vps_max_dec_pic_buffering[ i ]ue(v)   vps_max_num_reorder_pics[ i ] ue(v)   vps_max_latency_increase[i ] ue(v)  }  vps_num_hrd_parameters ue(v)  for( i = 0; i <vps_num_hrd_parameters; i++ ) {   operation_point_layer_ids( i )  hrd_parameters( i = = 0, vps_max_sub_layers_minus1 )  } vps_extension_flag u(1)  if( vps_extension_flag )   while(more_rbsp_data( ) )    vps_extension_data_flag u(1)  } rbsp_trailing_bits( ) }

The italicized portions of Table 3 and other syntax tables or semanticsdescriptions throughout this disclosure may indicate differences fromHEVC Working Draft 8. In accordance with one or more techniques of thisdisclosure, the semantics for the following syntax elements of the VPSmay be changed as follows. The semantics for other syntax elements ofthe VPS may remain the same as in HEVC Working Draft 8.

-   -   vps_max_dec_pic_buffering[i] specifies the required size of the        decoded picture buffer in units of picture storage buffers when        TargetDecHighestTid is equal to i. The value of        vps_max_dec_pic_buffering[i] shall be in the range of 0 to        MaxDpbSize (as specified in subclause A.4), inclusive. When i is        greater than 0, vps_max_dec_pic_buffering[i] shall be equal to        or greater than vps_max_dec_pic_buffering[i−1].    -   vps_max_num_reorder_pics[i] indicates the maximum allowed number        of pictures preceding any picture in decoding order and        succeeding that picture in output order when TargetDecHighestTid        is equal to i. The value of vps_max_num_reorder_pics[i] shall be        in the range of 0 to vps_max_dec_pic_buffering[i], inclusive.        When i is greater than 0, vps_max_num_reorder_pics[i] shall be        equal to or greater than vps_max_num_reorder_pics[i−1].    -   vps_max_latency_increase[i] not equal to 0 is used to compute        the value of MaxLatencyPictures[i] as specified by setting        MaxLatencyPictures[i] to        vps_max_num_reorder_pics[i]+vps_max_latency_increase[i]. When        vps_max_latency_increase[i] is not equal to 0, the value of        MaxLatencyPictures[i] specifies the maximum number of pictures        that can precede any picture in the coded video sequence in        output order and follow that picture in decoding order when        TargetDecHighestTid is equal to i. When        vps_max_latency_increase[i] is equal to 0, no corresponding        limit is expressed. The value of vps_max_latency_increase[i]        shall be in the range of 0 to 2³²−2, inclusive.

As shown above, the semantics of vps_max_dec_buffering[i],vps_max_num_reorder_pics[i], and vps_max_latency_increase[i] may bedefined with reference to TargetDecHighestTid. In contrast, HEVC WorkingDraft 8 defines vps_max_dec_pic_buffering[i],vps_max_num_reorder_pics[i], and vps_max_latency_increase[i] withreference to HighestTid, where HighestTid is not defined.

As shown in the example syntax of Table 3, the VPS includes pairs ofoperation_point_layer_ids( ) syntax structures and hrd_parameters( )syntax structures. The hrd_parameters( ) syntax structures includesyntax elements that specify sets of HRD parameters. Anoperation_point_layer_ids( ) syntax structure includes syntax elementsthat identify a set of operation points. The set of HRD parametersspecified in a hrd_parameters( ) syntax structure may be applicable tothe operation points identified by the syntax elements in thecorresponding operation_point_layer_ids( ) syntax structure. Table 4,below, provides an example syntax for an operation_point_layer_ids( )syntax structure.

TABLE 4 Operation Point Layer IDs De- operation_point_layer_ids( opIdx ){ scriptor  op_num_layer_id_values_minus1[ opIdx ] ue(v)  for( i = 0; i<= op_num_layer_id_values_minus1[ opIdx ];  i++)   op_layer_id[ opIdx ][i ] u(6) }

Section 7.4.4 of HEVC Working Draft 8 describes the semantics of anop_point syntax structure. In accordance with the one or more techniquesof this disclosure, section 7.4.4 of HEVC Working Draft 8 may be changedas follows to provide semantics for the operation_point_layer_ids( )syntax structure of Table 4.

-   -   The operation_point_layer_ids(opIdx) syntax structure specifies        the set of nuh_reserved_zero_(—)6 bits values included in the        OpLayerIdSet of the operation points to which the opIdx-th        hrd_parameters( ) syntax structure in the video parameter set        applies.    -   op_num_layer_id_values_minus1[opIdx] plus 1 specifies the number        of nuh_reserved_zero_(—)6 bits values included in the        OpLayerIdSet of the operation points to which the opIdx-th        hrd_parameters( ) syntax structure in the video parameter set        applies. op_num_layer_id_values_minus1[opIdx] shall be less than        or equal to 63. In bitstreams conforming to this Specification,        op_num_layer_id_values_minus1[opIdx] shall be equal to 0        Although the value of op_num_layer_id_values_minus1[opIdx] is        required to be equal to 0 in this version of this Specification,        decoders shall allow other values to appear in the        op_num_layer_id_values_minus1[opIdx] syntax.    -   op_layer_id[opIdx][i] specifies the i-th value of        nuh_reserved_zero_(—)6 bits included in the OpLayerIdSet of the        operation points to which the opIdx-th hrd_parameters( ) syntax        structure in the video parameter set applies. No value of        op_layer_id[opIdx][i] shall be equal to op_layer_id[opIdx][j]        when i is not equal to j and both i and j are in the range of 0        to op_num_layer_id_values_minus1, inclusive. op_layer_id[0][0]        is inferred to be equal to 0.

As indicated above, the op_num_layer_id_values_minus1[opIdx] syntaxelement, plus 1, specifies the number of nuh_reserved_zero_(—)6 bitsvalues included in the OpLayerIdSet of the operation points to which theopIdx-th hrd_parameters( ) syntax structure in the video parameter setapplies. In contrast, HEVC Working Draft 8 provides theop_num_layer_id_values_minus1[opIdx] syntax element, plus 1, specifiesthe number of nuh_reserved_zero_(—)6 bits values included in theoperation point identified by opIdx. Similarly, in the example of Table4, the op_layer_id[opIdx][i] syntax element specifies the i-th value ofnuh_reserved_zero_(—)6 bits included in the OpLayerIdSet of theoperation points to which the opIdx-th hrd_parameters( ) syntaxstructure in the video parameter set applies. In contrast, HEVC WorkingDraft 8 provides that the op_layer_id[opIdx][i] syntax element specifiesthe i-th value of nuh_reserved_zero_(—)6 bits included in the operationpoint identified by opIdx.

Section 7.4.2.2 of HEVC Working Draft 8 describes semantics for the SPS.In accordance with one or more techniques of this disclosure, thefollowing changes may be made to section 7.4.2.2 of HEVC Working Draft8. Semantics for other syntax elements of SPS may be the same as in HEVCWorking Draft 8:

-   -   sps_max_dec_pic_buffering[i] specifies the maximum required size        of the decoded picture buffer in units of picture storage        buffers when TargetDecHighestTid is equal to i. The value of        sps_max_dec_pic_buffering[i] shall be in the range of 0 to        MaxDpbSize (as specified in subclause A.4), inclusive. When i is        greater than 0, sps_max_dec_pic_buffering[i] shall be equal to        or greater than sps_max_dec_pic_buffering[i−1]. The value of        sps_max_dec_pic_buffering[i] shall be less than or equal to        vps_max_dec_pic_buffering[i] for each value of i.    -   sps_max_num_reorder_pics[i] indicates the maximum allowed number        of pictures preceding any picture in decoding order and        succeeding that picture in output order when TargetDecHighestTid        is equal to i. The value of sps_max_num_reorder_pics[i] shall be        in the range of 0 to sps_max_dec_pic_buffering[i], inclusive.        When i is greater than 0, sps_max_num_reorder_pics[i] shall be        equal to or greater than sps_max_num_reorder_pics[i−1]. The        value of sps_max_num_reorder_pics[i] shall be less than or equal        to vps_max_num_reorder_pics[i] for each value of i.    -   sps_max_latency_increase[i] not equal to 0 is used to compute        the value of MaxLatencyPictures[i] as specified by setting        MaxLatencyPictures[i] equal to        sps_max_num_reorder_pics[i]+sps_max_latency_increase[i]. When        sps_max_latency_increase[i] is not equal to 0, the value of        MaxLatencyPictures[i] specifies the maximum number of pictures        that can precede any picture in the coded video sequence in        output order and follow that picture in decoding order when        TargetDecHighestTid is equal to i. When        sps_max_latency_increase[i] is equal to 0, no corresponding        limit is expressed. The value of sps_max_latency_increase[i]        shall be in the range of 0 to 2³²−2, inclusive. The value of        sps_max_latency_increase[i] shall be less than or equal to        vps_max_latency_increase[i] for each value of i.

As shown above, the semantics of sps_max_dec_pic_buffering[i],sps_max_num_reorder_pics[i], and sps_max_latency_increase[i] are definedin terms of TargetDecHighestTid. TargetDecHighestTid is determined asdescribed elsewhere in this disclosure. In contrast, HEVC Working Draft8 defines the semantics of sps_max_dec_pic_buffering[i],sps_max_num_reorder_pics[i], and sps_max_latency_increase[i] withreference to HighestTid, which is not defined.

Section 7.4.5.1 of HEVC Working Draft 8 describes general slice headersemantics. In accordance with one or more techniques of this disclosure,the following changes may be made to section 7.4.5.1 of HEVC WorkingDraft 8. Other portions of section 7.4.5.1 of HEVC Working Draft 8 mayremain the same.

-   -   no_output_of_prior_pics_flag specifies how the        previously-decoded pictures in the decoded picture buffer are        treated after decoding of an IDR or a BLA picture. See Annex C.        When the current picture is a CRA picture, or the current        picture is an IDR or BLA picture that is the first picture in        the bitstream, the value of no_output_of_prior_pics_flag has no        effect on the decoding process. When the current picture is an        IDR or BLA picture that is not the picture in the bitstream, and        the value of pic_width_in_luma_samples or        pic_height_in_luma_samples or        sps_max_dec_pic_buffering[TargetDecHighestTid] derived from the        active sequence parameter set is different from the value of        pic_width_in_luma_samples or pic_height_in_luma_samples or        sps_max_dec_pic_buffering[TargetDecHighestTid] derived from the        sequence parameter set active for the preceding picture,        no_output_of_prior_pics_flag equal to 1 may (but should not) be        inferred by the decoder, regardless of the actual value of        no_output_of_prior_pics_flag.

As shown above, the semantics of no_output_of_prior_pics_flag aredefined with reference tosps_max_dec_pic_buffering[TargetDecHighestTid]. TargetDecHighestTid isdetermined as described elsewhere in this disclosure. In contrast, HEVCWorking Draft 8 defines the semantics of no_output_of_prior_pics_flagswith reference to sps_max_dec_pic_buffering[HighestTid], whereHighestTid is not defined.

Section 8.1 of HEVC Working Draft 8 describes a general decodingprocess. In accordance with one or more techniques of this disclosure,the general decoding process of HEVC Working Draft 8 may be changed asfollows.

-   -   The input of this process is a bitstream and the output is a        list of decoded pictures.    -   The set TargetDecLayerIdSet, which specifies the set of values        for nuh_reserved_zero_(—)6 bits of VCL NAL units to be decoded,        is specified as follows:        -   If some external means not specified in this Specification            is available to set TargetDecLayerIdSet, TargetDecLayerIdSet            is set by the external means.        -   Otherwise if the decoding process is invoked in a bitstream            conformance test as specified in subclause C.1,            TargetDecLayerIdSet is set as specified in subclause C.1.        -   Otherwise, TargetDecLayerIdSet contains only one value for            nuh_reserved_zero_(—)6 bits, which is equal to 0.    -   The variable TargetDecHighestTid, which identifies the highest        temporal sub-layer to be decoded, is specified as follows:        -   If some external means not specified in this Specification            is available to set TargetDecHighestTid, TargetDecHighestTid            is set by the external means.        -   Otherwise if the decoding process is invoked in a bitstream            conformance test as specified in subclause C.1,            TargetDecHighestTid is set as specified in subclause C.1.        -   Otherwise, TargetDecHighestTid is set to            sps_max_sub_layers_minus1.    -   The sub-bitstream extraction process as specified in subclause        10.1 is applied with TargetDecHighestTid and TargetDecLayerIdSet        as inputs and the output is assigned to a bitstream referred to        as BitstreamToDecode.    -   The following applies to each coded picture (referred to as the        current picture, which is denoted by the variable CurrPic) in        BitstreamToDecode.    -   Depending on the value of chroma_format_idc, the number of        sample arrays of the current picture is as follows.        -   If chroma_format_idc is equal to 0, the current picture            consists of 1 sample array S_(L).        -   Otherwise (chroma_format_idc is not equal to 0), the current            picture consists of 3 sample arrays S_(L), S_(Cb), S_(Cr).    -   The decoding process for the current picture takes the syntax        elements and upper-case variables from clause 7 as input. When        interpreting the semantics of each syntax element in each NAL        unit and “the bitstream” or part thereof (e.g., a coded video        sequence) is involved, the bitstream or part thereof means        BitstreamToDecode or part thereof.    -   The decoding process is specified such that all decoders shall        produce numerically identical results. Any decoding process that        produces identical results to the process described herein        conforms to the decoding process requirements of this        Specification.    -   When the current picture is a CRA picture, the following        applies:        -   If some external means not specified in this Specification            is available to set the variable HandleCraAsBlaFlag to a            value, HandleCraAsBlaFlag is set to the value provided by            the external means.        -   Otherwise, the value of HandleCraAsBlaFlag is set to 0.    -   When the current picture is a CRA picture and HandleCraAsBlaFlag        is equal to 1, the following applies during the parsing and        decoding processes for each coded slice NAL unit:        -   The value of nal_unit_type is set to BLA_W_LP.        -   The value of no_output_of_prior_pics_flag is set to 1.            -   NOTE 1—Decoder implementations may choose to set the                value of no_output_of_prior_pics_flag to 0 when the                setting does not affect decoding of the current picture                and the following pictures in decoding order, e.g. when                there is always a picture storage buffer available when                needed.    -   Each picture referred to in this clause is a complete coded        picture.    -   Depending on the value of separate_colour_plane_flag, the        decoding process is structured as follows.        -   If separate_colour_plane_flag is equal to 0, the decoding            process is invoked a single time with the current picture            being the output.        -   Otherwise (separate_colour_plane_flag is equal to 1), the            decoding process is invoked three times. Inputs to the            decoding process are all NAL units of the coded picture with            identical value of colour_plane_id. The decoding process of            NAL units with a particular value of colour_plane_id is            specified as if only a coded video sequence with monochrome            color format with that particular value of colour_plane_id            would be present in the bitstream. The output of each of the            three decoding processes is assigned to the 3 sample arrays            of the current picture with the NAL units with            colour_plane_id equal to 0 being assigned to S_(L), the NAL            units with colour_plane_id equal to 1 being assigned to            S_(Cb), and the NAL units with colour_plane_id equal to 2            being assigned to S_(Cr).            -   NOTE 1—The variable ChromaArrayType is derived as 0 when                separate_colour_plane_flag is equal to 1 and                chroma_format_idc is equal to 3. In the decoding                process, the value of this variable is evaluated                resulting in operations identical to that of monochrome                pictures with chroma_format_idc being equal to 0.

The decoding process operates as follows for the current pictureCurrPic:

-   -   1. The decoding of NAL units is specified in subclause 8.2.    -   2. The processes in subclause 8.3 specify decoding processes        using syntax elements in the slice layer and above:        -   Variables and functions relating to picture order count are            derived in subclause 8.3.1 (which only needs to be invoked            for the first slice of a picture).        -   The decoding process for reference picture set in subclause            8.3.2 is invoked, wherein reference pictures may be marked            as “unused for reference” or “used for long-term reference”            (which only needs to be invoked for the first slice of a            picture).        -   When the current picture is a BLA picture or is a CRA            picture that is the first picture in the bitstream, the            decoding process for generating unavailable reference            pictures specified in subclause 8.3.3 is invoked (which only            needs to be invoked for the first slice of a picture).        -   PicOutputFlag is set as follows:            -   If the current picture is a TFD picture and the previous                RAP picture in decoding order is a BLA picture or is a                CRA picture that is the first coded picture in the                bitstream, PicOutputFlag is set equal to 0.            -   Otherwise, PicOutputFlag is set equal to                pic_output_flag.        -   At the beginning of the decoding process for each P or B            slice, the decoding process for reference picture lists            construction specified in subclause 8.3.4 is invoked for            derivation of reference picture list 0 (RefPicList0), and            when decoding a B slice, reference picture list 1            (RefPicList1).        -   After all slices of the current picture have been decoded,            the decoded picture is marked as “used for short-term            reference”.    -   3. The processes in subclauses 8.4, 8.5, 8.6, and 8.7 specify        decoding processes using syntax elements in the coding tree unit        layer and above.

As indicated elsewhere in this disclosure, in HEVC Working Draft 8, whenthe decoding process is invoked for bitstream conformance test, thesemantics of syntax elements are not clearly specified as the values ofTargetDecLayerIdSet and TargetDecHighestTid are not properly set. Themodifications shown above to the general decoding process may remedythis issue. As shown above, when the general decoding process is invokedfor a bitstream conformance test, the values of TargetDecLayerIdSet andTargetDecHighestTid are set as specified in subclause C.1. As describedbelow, a modified version of subclause C.1 may set TargetDecLayerIdSetto the set of nuh_reserved_zero_(—)6 bits values present in thesub-bitstream corresponding to the operation point under test. Themodified version of subclause C.1 may set TargetDecHighestTid to thegreatest TemporalId value present in the sub-bitstream corresponding tothe operation point under test.

In this way, a device, such as video decoder 30, may perform a decodingprocess as part of performing a bitstream conformance test. Performingthe decoding process may comprise performing a bitstream extractionprocess to extract, from a bitstream, an operation point representationof an operation point defined by a target set of layer identifiers and atarget highest temporal identifier. The target set of layer identifiersmay contain values of layer identifier syntax elements present in theoperation point representation, the target set of layer identifiersbeing a subset of values of layer identifier syntax elements of thebitstream. The target highest temporal identifier may be equal to agreatest temporal identifier present in the operation pointrepresentation, the target highest temporal identifier being less thanor equal to a greatest temporal identifier present in the bitstream.Furthermore, the device may decode NAL units of the operation pointrepresentation.

As indicated in the modifications to section 8.1 above, the decodingprocess is not necessarily performed as part of the bitstreamconformance test. In some instances where the decoding process is notperformed as part of a bitstream conformance test, a device may performthe bitstream extraction process to extract, from the bitstream, anoperation point representation of an operation point. In this case, 0may be the only value of layer identifier syntax elements (e.g.,nuh_reserved_zero_(—)6 bits) present in the operation pointrepresentation, and the greatest temporal identifier present in thebitstream is equal to a greatest temporal identifier present in theoperation point representation of the operation point. The device maydecode NAL units of the operation point representation of the secondoperation point.

Alternatively, the device may receive, from an external source, a targetset of layer identifiers and a target highest temporal identifier. Thetarget set of layer identifiers may contain values of layer identifiersyntax elements present in an operation point representation of anoperation point that is defined by the target set of layer identifiersand the target highest temporal identifier. The target highest temporalidentifier may be equal to a greatest temporal identifier present in theoperation point representation of the operation point. Furthermore, thedevice may perform the bitstream extraction process to extract, from thebitstream, the operation point representation of the operation point. Inaddition, the device may decode NAL units of the operation pointrepresentation of the operation point.

Furthermore, in accordance with one or more techniques of thisdisclosure, the sub-bitstream extraction process described in subclause10.1 of HEVC Working Draft 8 may be changed as follows.

-   -   It is requirement of bitstream conformance that any        sub-bitstream that is included in the output of the process        specified in this subclause with tIdTarget equal to any value in        the range of 0 to 6, inclusive, and with layerIdSetTarget        containing only the value 0 shall be conforming to this        Specification.    -   NOTE—A conforming bitstream contains one or more coded slice NAL        units with nuh_reserved_zero_(—)6 bits equal to 0 and TemporalId        equal to 0.    -   Inputs to this process are a variable tIdTarget and a set        layerIdSetTarget.    -   Output of this process is a sub-bitstream.    -   The sub-bitstream is derived by removing from the bitstream all        NAL units with TemporalId greater than tIdTarget or        nuh_reserved_zero_(—)6 bits not among the values in        layerIdSetTarget.

In subclause 10.1 of HEVC Working Draft 8, the variable nametargetDecLayerIdSet is used where layerIdSetTarget is used above. Thechanges shown above to subclause 10.1 of HEVC Working Draft to uselayerIdSetTarget may serve to clarify that there may be a distinctionbetween the set of layer identifiers used in the sub-bitstreamextraction process and targetDecLayerIdSet, which, as describedelsewhere in this disclosure, has a particular definition.

Furthermore, in accordance with one or more techniques of thisdisclosure, the general tier and level specifications of section A.4.1of HEVC Working Draft 8 may be changed as follows. In this disclosure, a“profile” may refer to a subset of the bitstream syntax. “Tiers” and“levels” may be specified within each profile. A level of a tier may bea specified set of constraints imposed on values of the syntax elementsin the bitstream. These constraints may be simple limits on values.

Alternatively, the constraints may take the form of constraints onarithmetic combinations of values (e.g., picture width multiplied bypicture height multiplied by number of pictures decoded per second). Alevel specified for a lower tier is more constrained than a levelspecified for a higher tier. In accordance with an example of thisdisclosure, the “general level specifications” section (i.e. sectionA.4.1) of HEVC Working Draft 8 is re-titled “General tier and levelspecifications,” and the text is changed as follows. Table A-1 mayremain the same as in HEVC Working Draft 8.

-   -   For purposes of comparison of tier capabilities, the tier with        general_tier_flag equal to 0 shall be considered to be a lower        tier than the tier with general_tier_flag equal to 1.    -   For purposes of comparison of level capabilities, for a specific        tier, a lower level has a lower value of general_level_idc.    -   The following is specified for expressing the constraints in        this annex.        -   Let access unit n be the n-th access unit in decoding order,            with the first access unit being access unit 0 (i.e. the            0-th access unit).        -   Let picture n be the coded picture or the corresponding            decoded picture of access unit n.        -   Let the variable fR be set to 1÷300.    -   Bitstreams conforming to a profile at a specified level shall        obey the following constraints for each bitstream conformance        test as specified in Annex C:        -   a) The nominal removal time of access unit n (with n>0) from            the CPB as specified in subclause C.2.2 satisfies the            constraint that t_(r,n)(n)−t_(r)(n−1) is equal to or greater            than Max(PicSizeInSamplesY÷MaxLumaSR, fR) for the value of            PicSizeInSamplesY of picture n−1, where MaxLumaSR is the            value specified in Table A-1 that applies to picture n−1.        -   b) The difference between consecutive output times of            pictures from the DPB as specified in subclause C.3.2            satisfies the constraint that            Δt_(o,dpb)(n)>=Max(PicSizeInSamplesY÷MaxLumaSR, fR) for the            value of PicSizeInSamplesY of picture n, where MaxLumaSR is            the value specified in Table A-1 for picture n, provided            that picture n is a picture that is output and is not the            last picture of the bitstream that is output.        -   c) PicSizeInSamplesY<=MaxLumaPS, where MaxLumaPS is            specified in Table A-1.        -   d) pic_width_in_luma_samples<=Sqrt(MaxLumaPS*8)        -   e) pic_height_in_luma_samples<=Sqrt(MaxLumaPS*8)        -   f)            sps_max_dec_pic_buffering[TargetDecHighestTid]<=MaxDpbSize,            where MaxDpbSize is derived as specified by the following:

if ( PicSizeInSamplesY <= ( MaxLumaPS >> 2) )  MaxDpbSize = Min( 4 *MaxDpbPicBuf, 16 ) else if ( PicSizeInSamplesY <= ( MaxLumaPS >> 1 ) ) MaxDpbSize = Min( 2 * MaxDpbPicBuf, 16 ) else if ( PicSizeInSamplesY <=( MaxLumaPS << 1) / 3 )  MaxDpbSize = Min( (3 * MaxDpbPicBuf) >> 1, 16 )else if ( PicSizeInSamplesY <= ( ( 3 * MaxLumaPS ) >> 2) )  MaxDpbSize =Min( (4 * MaxDpbPicBuf) / 3, 16 ) else  MaxDpbSize = MaxDpbPicBuf

-   -    where MaxLumaPS is specified in Table A-1 and MaxDpbPicBuf is        equal to 6.    -   Table A-1 specifies the limits for each level of each tier. The        use of the MinCR parameter column of Table A-1 is specified in        subclause A.4.2.    -   A tier and level to which the bitstream conforms shall be        indicated by the syntax elements general_tier_flag and        general_level_idc as follows.        -   general_tier_flag equal to 0 indicates conformance to the            Main tier, and general_tier_flag equal to 1 indicates            conformance to the High tier, according to the tier            constraint specifications in Table A-1. general_tier_flag            shall be equal to 0 for levels below level 4 (corresponding            to the entries in Table A-1 marked with “-”). Level limits            other than MaxBR and MaxCPB in Table A-1 are common for both            the Main tier and the High tier.        -   general_level_idc shall be set equal to a value of 30 times            the level number specified in Table A-1.

As indicated in item (f) above, bitstreams conforming to a profile at aspecified level obey the constraint thatsps_max_dec_pic_buffering[TargetDecHighestTid]<=MaxDpbSize.TargetDecHighestTid may be defined in the manner described elsewhere inthis disclosure. In contrast, HEVC Working Draft 8 indicates for item(f) that bitstreams conforming to a profile at a specified level obeythe constraint thatsps_max_dec_pic_buffering[sps_max_temporal_layers_minus1]<=MaxDpbSize.As indicated elsewhere in this disclosure, the parameterssps_max_dec_pic_buffering [i] may not be properly selected in levelrestrictions. Replacing sps_max_temporal_layers_minus1 withTargetDecHighestTid as the index i of sps_max_dec_pic_buffering[i] may,in accordance with one or more techniques of this disclosure, ensurethat level restrictions are consistently selected with i equal to theclearly-specified value of TargetDecHighestTid.

In this way, a decoding process of a HRD may decode, from a SPS, anarray of syntax elements (e.g., sps_max_dec_pic_buffering[ ]) where eachof the syntax elements in the array indicates a maximum required size ofa DPB of the HRD. Furthermore, when a device performs a HRD operation,the device may determine, based on the target highest temporalidentifier (e.g., TargetDecHighestTid), a particular syntax element inthe array (e.g., sps_max_dec_pic_buffering[TargetDecHighestTid]).Furthermore, the device may determine that the bitstream is not inconformance with the video coding standard when a value of theparticular syntax element is greater than a maximum DPB size (e.g.,MaxDpbSize).

Furthermore, in accordance with one or more example techniques of thisdisclosure, section A.4.2 of HEVC Working Draft 8 may be changed asfollows. Section A.4.2 of HEVC Working Draft 8 describesprofile-specific level limits for the Main profile. Table A-2 may remainthe same as in HEVC Working Draft 8.

-   -   Bitstreams conforming to the Main profile at a specified tier        and level shall obey the following constraints for the bitstream        conformance tests as specified in Annex C:        -   a) The number of slices (with dependent_slice_flag equal to            either 0 or 1) in a picture is less than or equal to            MaxSlicesPerPicture, where MaxSlicesPerPicture is specified            in Table A-1.        -   b) For the VCL HRD parameters,            -   BitRate[SchedSelIdx]<=cpbBrVclFactor*MaxBR and            -   CpbSize[SchedSelIdx]<=cpbBrVclFactor*MaxCPB for at least                one value of SchedSelIdx, where cpbBrVclFactor is                specified in Table A-2 and BitRate[SchedSelIdx] and                CpbSize[SchedSelIdx] are given as follows.                -   If vcl_hrd_parameters_present_flag is equal to 1,                    BitRate[SchedSelIdx] and CpbSize[SchedSelIdx] are                    given by Equations E-45 and E-46, respectively,                    using the syntax elements that are selected as                    specified in subclause C.1.                -   Otherwise (vcl_hrd_parameters_present_flag is equal                    to 0), BitRate[SchedSelIdx] and CpbSize[SchedSelIdx]                    are inferred as specified in subclause E.2.3 for VCL                    HRD parameters.            -   MaxBR and MaxCPB are specified in Table A-1 in units of                cpbBrVclFactor bits/s and cpbBrVclFactor bits,                respectively. The bitstream shall satisfy these                conditions for at least one value of SchedSelIdx in the                range 0 to cpb_cnt_minus1[TargetDecHighestTid],                inclusive.        -   c) For the NAL HRD parameters,            -   BitRate[SchedSelIdx]<=cpbBrNalFactor*MaxBR and                CpbSize[SchedSelIdx]<=cpbBrNalFactor*MaxCPB for at least                one value of SchedSelIdx, where cpbBrNalFactor is                specified in Table A-2 and BitRate[SchedSelIdx] and                CpbSize[SchedSelIdx] are given as follows.                -   If nal_hrd_parameters_present_flag is equal to 1,                    BitRate[SchedSelIdx] and CpbSize[SchedSelIdx] are                    given by Equations E-45 and E-46, respectively,                    using the syntax elements that are selected as                    specified in subclause C.1.                -   Otherwise (nal_hrd_parameters_present_flag is equal                    to 0), BitRate[SchedSelIdx] and CpbSize[SchedSelIdx]                    are inferred as specified in subclause E.2.3 for NAL                    HRD parameters.            -   MaxBR and MaxCPB are specified in Table A-1 in units of                cpbBrNalFactor bits/s and cpbBrNalFactor bits,                respectively. The bitstream shall satisfy these                conditions for at least one value of SchedSelIdx in the                range 0 to cpb_cnt_minus1[TargetDecHighestTid],                inclusive.        -   d) The sum of the NumBytesInNALunit variables for access            unit 0 is less than or equal to            -   1.5*(Max(PicSizeInSamplesY,                fR*MaxLumaSR)+MaxLumaSR*(t_(r)(0)−t_(r,n)(0)))÷MinCR for                the value of PicSizeInSamplesY of picture 0, where                MaxLumaPR and MinCR are the values specified in Table                A-1 that apply to picture 0.        -   e) The sum of the NumBytesInNALunit variables for access            unit n with n>0 is less than or equal to            -   1.5*MaxLumaSR*(t_(r)(n)−t_(r)(n−1))÷MinCR, where                MaxLumaSR and MinCR are the values specified in Table                A-1 that apply to picture n.        -   f) For level 5 and higher levels, the variable CtbSizeY            shall be equal to 32 or 64.        -   g) The value of NumPocTotalCurr shall be less than or equal            to 8.        -   h) The value of num_tile_columns_minus1 shall be less than            MaxTileCols and num_tile_rows_minus1 shall be less than            MaxTileRows, where MaxTileCols and MaxTileRows are as            specified in Table A-1.

As indicated elsewhere in this disclosure, the parameterscpb_cnt_minus1[i] may not be properly selected in level restrictions.HEVC Working Draft 8 specifies that “the bitstream shall satisfy theseconditions for at least one value of SchedSelIdx in the range 0 tocpb_cnt_minus1, inclusive . . . ” Specifying TargetDecHighestTid as theindex i of cpb_cnt_minus1[i] may, in accordance with one or moretechniques of this disclosure, ensure that level restrictions areconsistently selected with i equal to the clearly-specified value ofTargetDecHighestTid.

Furthermore, in accordance with one or more techniques of thisdisclosure, the general subclause C.1 in Annex C of HEVC Working Draft 8may be modified. The figures C-1 and C-2 of subclause C.1 of HEVCWorking Draft 8 may remain the same as in HEVC WD8. The text ofsubclause C.1 of HEVC Working Draft 8 may be changed as follows.

-   -   This annex specifies the hypothetical reference decoder (HRD)        and its use to check bitstream and decoder conformance.    -   Two types of bitstreams are subject to HRD conformance checking        for this Specification. The first type of bitstream, called Type        I bitstream, is a NAL unit stream containing only the VCL NAL        units and NAL units with nal_unit_type equal to FD_NUT (filler        data NAL units) for all access units in the bitstream. The        second type of bitstream, called a Type II bitstream, contains,        in addition to the VCL NAL units and filler data NAL units for        all access units in the bitstream, at least one of the        following:        -   additional non-VCL NAL units other than filler data NAL            units,        -   all leading_zero_(—)8 bits, zero_byte,            start_code_prefix_one_(—)3 bytes, and trailing_zero_(—)8            bits syntax elements that form a byte stream from the NAL            unit stream (as specified in Annex B).    -   Figure C-1 shows the types of bitstream conformance points        checked by the HRD.    -   The syntax elements of non-VCL NAL units (or their default        values for some of the syntax elements) required for the HRD are        specified in the semantic subclauses of clause 7, Annexes D and        E.    -   Two types of HRD parameters (NAL HRD parameters and VCL HRD        parameters) are used. The HRD parameters are signaled through        the video parameter set syntax structure or through video        usability information as specified in subclauses E.1 and E.2,        which is part of the sequence parameter set syntax structure.    -   Multiple tests may be needed for checking the conformance of a        bitstream. For each test, the following steps apply in the order        listed:        -   1. An operation point under test, denoted as TargetOp, is            selected. TargetOp is identified by OpLayerIdSet equal to            targetOpLayerIdSet and OpTid equal to targetOpTid.            targetOpLayerIdSet contains the set of values for            nuh_reserved_zero_(—)6 bits present in the bitstream subset            associated with TargetOp and shall be a subset of values for            nuh_reserved_zero_(—)6 bits present in the bitstream under            test. targetOpTid is equal to the greatest TemporalId            present in the bitstream subset associated with TargetOp and            shall be less than or equal to the greatestTemporalId            present in the bitstream under test.        -   2. TargetDecLayerIdSet is set to targetOpLayerIdSet,            TargetDecHighestTid is set to targetOpTid, and            BitstreamToDecode is set to the output of the sub-bitstream            extraction process as specified in subclause 10.1 with            TargetDecHighestTid and TargetDecLayerIdSet as inputs.        -   3. The hrd_parameters( )) syntax structure and the            sub_layer_hrd_parameters( ) syntax structure applicable to            TargetOp are selected. If TargetDecLayerIdSet contains only            the value 0, the hrd_parameters( )) syntax structure in the            active sequence parameter set is selected. Otherwise, the            hrd_parameters( )) syntax structure that is in the active            sequence parameter set (or provided through an external            means) and for which the set of values specified by            op_layer_id[opIdx][i] for i in the range of 0 to            op_num_layer_id_values_minus1[opIdx], inclusive, is            identical to TargetDecLayerIdSet is selected. Within the            selected hrd_parameters( ) syntax structure, if            BitstreamToDecode is a Type I bitstream, the            sub_layer_hrd_parameters(TargetDecHighestTid) syntax            structure that immediately follows the condition            -   “if(vcl_hrd_parameters_present_flag)” is selected (in                this case the variable NalHrdModeFlag is set equal to                0), otherwise (BitstreamToDecode is a Type II                bitstream), the                sub_layer_hrd_parameters(TargetDecHighestTid) syntax                structure that either immediately follows the condition                “if(vcl_hrd_parameters_present_flag)” (in this case the                variable NalHrdModeFlag is set equal to 0) or the                condition “if(nal_hrd_parameters_present_flag)” (in this                case the variable NalHrdModeFlag is set equal to 1) is                selected, and all non-VCL NAL units except for filler                data NAL units are discarded from BitstreamToDecode in                the former case and the result is assigned to                BitstreamToDecode.        -   4. An access unit associated with a buffering period SEI            message applicable to TargetOp is selected as the HRD            initialization point and referred to as access unit 0.        -   5. SEI messages including timing information are selected.            The buffering period SEI message that is coded in access            unit 0 and applies to TargetOp, as indicated by the            applicable_operation_points( ) syntax structure, is            selected. For each access unit in BitstreamToDecode starting            from access unit 0, the picture timing SEI message that is            associated with the access unit and applies to TargetOp, as            indicated by the applicable_operation_points( ) syntax            structure, is selected, and when SubPicCpbFlag is equal to 1            and sub_pic_cpb_params_in_pic_timing_sei_flag is equal to 0,            the sub-picture timing SEI messages that are associated with            decoding units in the access unit and apply to TargetOp, as            indicated by the applicable_operation_points( ) syntax            structures, are selected.        -   6. A value of SchedSelIdx is selected. The selected            SchedSelIdx shall be in the range of 0 to            cpb_cnt_minus1[TargetDecHighestTid], inclusive, where            cpb_cnt_minus1[TargetDecHighestTid] is found in the            sub_layer_hrd_parameters(TargetDecHighestTid) syntax            structure as selected above.        -   7. The initial CPB removal delay and delay offset is            selected and TFD access units associated with access unit 0            may be discarded from BitstreamToDecode. If the coded            picture in access unit 0 has nal_unit_type equal to CRA_NUT            or BLA_W_LP, and rap_cpb_params_present_flag in the selected            buffering period SEI message is equal to 1, either the            default initial CPB removal delay and delay offset            represented by the initial_cpb_removal_delay[SchedSelIdx]            and initial_cpb_removal_delay_offset[SchedSelIdx]            corresponding to NalHrdModeFlag (in this case the variable            DefaultInitCpbParamsFlag is set equal to 1) or the            alternative initial CPB removal delay and delay offset            represented by the            initial_alt_cpb_removal_delay[SchedSelIdx] and            initial_alt_cpb_removal_delay_offset[SchedSelIdx]            corresponding to NalHrdModeFlag (in this case the variable            DefaultInitCpbParamsFlag is set equal to 0) is selected, and            TFD access units associated with access unit 0 are discarded            from BitstreamToDecode in the latter case and the result is            assigned to BitstreamToDecode. Otherwise, the default            initial CPB removal delay and delay offset is selected (in            this case the variable DefaultInitCpbParamsFlag is set equal            to 1).    -   The number of bitstream conformance tests carried out is equal        to N1*N2*N3*(N4*2+N5), where the values of N1, N2, N3, N4 and N5        are specified as follows.        -   N1 is the number of operation points contained in the            bitstream under test.        -   If BitstreamToDecode is a Type I bitstream, N2 is equal to            1, otherwise (BitstreamToDecode is a Type II bitstream) N2            is equal to 2.        -   N3 is equal to cpb_cnt_minus1[TargetDecHighestTid]+1.        -   N4 is the number of access units associated with buffering            period SEI messages applicable to TargetOp in            BitstreamToDecode, where the coded picture in each of these            access units has nal_unit_type equal to CRA_NUT or BLA_W_LP,            and the associated buffering period SEI message applicable            to TargetOp has rap_cpb_params_present_flag equal to 1.        -   N5 is the number of access units associated with buffering            period SEI messages applicable to TargetOp in            BitstreamToDecode, where the coded picture in each of these            access units has nal_unit_type not equal to one of CRA_NUT            and BLA_W_LP, or the associated buffering period SEI message            applicable to TargetOp has rap_cpb_params_present_flag equal            to 0.    -   When BitstreamToDecode is a Type II bitstream, if the        sub_layer_hrd_parameters(TargetDecHighestTid) syntax structure        that immediately follows the condition        “if(vcl_hrd_parameters_present_flag)” is selected, the test is        conducted at the Type I conformance point shown in Figure C-1,        and only VCL and filler data NAL units are counted for the input        bit rate and CPB storage; otherwise (the        sub_layer_hrd_parameters(TargetDecHighestTid) syntax structure        that immediately follows the condition        “if(nal_hrd_parameters_present_flag)” is selected, the tests is        conducted at the Type II conformance point shown in Figure C-1,        and all NAL units (of a Type II NAL unit stream) or all bytes        (of a byte stream) are counted for the input bit rate and CPB        storage.        -   NOTE 3—NAL HRD parameters established by a value of            SchedSelIdx for the Type II conformance point shown in            Figure C-1 are sufficient to also establish VCL HRD            conformance for the Type I conformance point shown in Figure            C-1 for the same values of InitCpbRemovalDelay[SchedSelIdx],            BitRate[SchedSelIdx], and CpbSize[SchedSelIdx] for the VBR            case (cbr_flag[SchedSelIdx] equal to 0). This is because the            data flow into the Type I conformance point is a subset of            the data flow into the Type II conformance point and            because, for the VBR case, the CPB is allowed to become            empty and stay empty until the time a next picture is            scheduled to begin to arrive. For example, when decoding a            coded video sequence conforming to one or more of the            profiles specified in Annex A using the decoding process            specified in clauses 2-9, when NAL HRD parameters are            provided for the Type II conformance point that not only            fall within the bounds set for NAL HRD parameters for            profile conformance in item c) of subclause A.4.2 but also            fall within the bounds set for VCL HRD parameters for            profile conformance in item b) of subclause A.4.2,            conformance of the VCL HRD for the Type I conformance point            is also assured to fall within the bounds of item b) of            subclause A.4.2.    -   All video parameter sets, sequence parameter sets and picture        parameter sets referred to in the VCL NAL units and the        corresponding buffering period and picture timing SEI messages        shall be conveyed to the HRD, in a timely manner, either in the        bitstream (by non-VCL NAL units), or by other means not        specified in this Specification.    -   In Annexes C, D, and E, the specification for “presence” of        non-VCL NAL units is also satisfied when those NAL units (or        just some of them) are conveyed to decoders (or to the HRD) by        other means not specified by this Specification. For the purpose        of counting bits, only the appropriate bits that are actually        present in the bitstream are counted.        -   NOTE 1—As an example, synchronization of a non-VCL NAL unit,            conveyed by means other than presence in the bitstream, with            the NAL units that are present in the bitstream, can be            achieved by indicating two points in the bitstream, between            which the non-VCL NAL unit would have been present in the            bitstream, had the encoder decided to convey it in the            bitstream.        -   When the content of a non-VCL NAL unit is conveyed for the            application by some means other than presence within the            bitstream, the representation of the content of the non-VCL            NAL unit is not required to use the same syntax as specified            in this Specification.            -   NOTE 2—When HRD information is contained within the                bitstream, it is possible to verify the conformance of a                bitstream to the requirements of this subclause based                solely on information contained in the bitstream. When                the HRD information is not present in the bitstream, as                is the case for all “stand-alone” Type I bitstreams,                conformance can only be verified when the HRD data is                supplied by some other means not specified in this                Specification.        -   The HRD contains a coded picture buffer (CPB), an            instantaneous decoding process, a decoded picture buffer            (DPB), and output cropping as shown in Figure C-2.        -   For each bitstream conformance test, the CPB size (number of            bits) is CpbSize[SchedSelIdx] as specified by Equation E-46,            where SchedSelIdx and the HRD parameters are selected as            specified above in this subclause. The DPB size (number of            picture storage buffers) is            sps_max_dec_pic_buffering[TargetDecHighestTid].        -   The variable SubPicCpbPreferredFlag is either specified by            external means, or when not specified by external means, set            to 0.        -   The variable SubPicCpbFlag is derived as follows:            SubPicCpbFlag=SubPicCpbPreferredFlag &&            sub_pic_cpb_params_present_flag  (C-1)    -    If SubPicCpbFlag is equal to 0, the CPB operates at access unit        level and each decoding unit is an access unit. Otherwise the        CPB operates at sub-picture level and each decoding unit is a        subset of an access unit.        -   The HRD operates as follows. Data associated with decoding            units that flow into the CPB according to a specified            arrival schedule are delivered by the HSS. The data            associated with each decoding unit are removed and decoded            instantaneously by the instantaneous decoding process at the            CPB removal time of the decoding unit. Each decoded picture            is placed in the DPB. A decoded picture is removed from the            DPB as specified in subclause C.3.1 or subclause C.5.2.        -   The operation of the CPB for each bitstream conformance test            is specified in subclause C.2. The instantaneous decoder            operation is specified in clauses 2-9. The operation of the            DPB for each bitstream conformance test is specified in            subclause C.3. The output cropping for each bitstream            conformance test is specified in subclause C.3.2 and            subclause C.5.2.        -   HSS and HRD information concerning the number of enumerated            delivery schedules and their associated bit rates and buffer            sizes is specified in subclauses E.1.1, E.1.2, E.2.1, and            E.2.2. The HRD is initialized as specified by the buffering            period SEI message as specified in subclauses D.1.1 and            D.2.1. The removal timing of decoding units from the CPB and            output timing of decoded pictures from the DPB are specified            in the picture timing SEI message as specified in subclauses            D.1.2 and D.2.1. All timing information relating to a            specific decoding unit shall arrive prior to the CPB removal            time of the decoding unit.        -   The requirements for bitstream conformance are specified in            subclause C.4, and the HRD is used to check conformance of            decoders as specified in subclause C.5.            -   NOTE 3—While conformance is guaranteed under the                assumption that all picture rates and clocks used to                generate the bitstream match exactly the values signaled                in the bitstream, in a real system each of these may                vary from the signaled or specified value.        -   All the arithmetic in this annex is done with real values,            so that no rounding errors can propagate. For example, the            number of bits in a CPB just prior to or after removal of a            decoding unit is not necessarily an integer.        -   The variable t_(c) is derived as follows and is called a            clock tick:            t _(c)=num_units_in_tick÷time_scale  (C-1)    -    The variable t_(c) _(—) _(sub) is derived as follows and is        called a sub-picture clock tick:        t _(c) _(—) _(sub) =t _(c)÷(tick_divisor_minus2+2)  (C-2)        -   The following is specified for expressing the constraints in            this annex:            -   Let access unit n be the n-th access unit in decoding                order with the first access unit being access unit 0                (i.e. the 0-th access unit).            -   Let picture n be the coded picture or the decoded                picture of access unit n.            -   Let decoding unit m be the m-th decoding unit in                decoding order with the first decoding unit being                decoding unit 0.

The modifications to section C.1 of HEVC Working Draft 8 above mayclarify the bitstream conformance tests. As indicated above, when thedecoding process is invoked for the bitstream conformance test in HEVCWorking Draft 8, the semantics of syntax elements are not clearlyspecified as the values of TargetDecLayerIdSet and TargetDecHighestTidare not properly set. The modifications to section C.1 clarify thedefinitions of TargetDecLayerIdSet and TargetDecHighestTid.

As shown in the above modifications to section C.1 of HEVC Working Draft8, a device may perform an HRD operation (such as a bitstreamconformance test) that selects an operation point, determines a targetset of layer identifiers (TargetDecLayerIdSet) of the operation pointand the highest temporal identifier (TargetDecHighestTid). Furthermore,in the HRD operation, the device may select a set of HRD parametersapplicable to the operation point and use the selected set of HRDparameters to configure a HRD that performs the decoding process. Theset of HRD parameters applicable to the particular operation point mayinclude parameters that specify an initial CPB removal delay, a CPBsize, a bit rate, an initial DPB output delay, a DPB size, and so on.The HRD operation may include performing a decoding process.

In some examples, the device may select, from among one or more sets ofHRD parameters (e.g., hrd_parameters( ) syntax structures) in a VPS anda set of HRD parameters in a SPS, the set of HRD parameters applicableto the operation point. In some examples, the device may determine theset of HRD parameters in the SPS is applicable to the particularoperation point when a layer identifier set of the operation pointcontains a set of all layer identifiers present in a coded videosequence associated with the SPS. Furthermore, in some examples, thedevice may select the set of HRD parameters in the SPS in response todetermining that the target layer identifier set (e.g.,TargetDecLayerIdSet) of the operation point contains only the value 0.In some examples, the device may select a set of HRD parameter in theVPS in response to determining that a set of layer identifiers (e.g.,op_layer_id[ ][ ]) is identical to the target layer identifier set(e.g., TargetDecLayerIdSet) of the operation point.

Furthermore, as shown in the above modifications to section C.1 of HEVCWorking Draft 8 and other portions of this disclosure, the device maydecode, from a SPS, the array of syntax elements(sps_max_dec_pic_buffering[ ]) that each indicate a maximum requiredsize of a DPB of the HRD. The device may determine, based on the targethighest temporal identifier, a particular syntax element in the array(i.e., sps_max_dec_pic_buffering[TargetDecHighestTid]). As indicatedabove, a number of picture storage buffers in the DPB is indicated bythe particular syntax element (i.e., the DPB size (number of picturestorage buffers) is sps_max_dec_pic_buffering[TargetDecHighestTid]).

In addition, a decoding process may decode a HRD parameters syntaxstructure (hrd_parameters( )) that includes the selected set of HRDparameters. The selected set of HRD parameters includes an array ofsyntax elements (cbp_cnt_minus1[ ]) that each indicate a number ofalternative CPB specifications in the bitstream. The modifications tosection C.1 of HEVC Working Draft 8 clarify that when a device performsa HRD operation, the device may select, based on the target highesttemporal identifier (TargetDecHighestTid), a particular syntax elementin the array (cpb_cnt_minus1[TargetDecHighestTid]) and may select ascheduler selection index (SchedSelIdx) in a range of 0 to a value ofthe particular syntax element. The device may determine, based at leastin part on the scheduler selection index, an initial CPB removal delayof a CPB of the HRD.

Section C.2.1 of HEVC Working Draft 8 relates to removal of picturesfrom the DPB for bitstream conformance. In accordance with one or moreexample techniques of this disclosure, section C.2.1 of HEVC WorkingDraft 8 may be changed as follows:

-   -   The specifications in this subclause apply independently to each        set of DPB parameters selected as specified in subclause C.1.    -   The removal of pictures from the DPB before decoding of the        current picture (but after parsing the slice header of the first        slice of the current picture) happens instantaneously at the CPB        removal time of the first decoding unit of access unit n        (containing the current picture) and proceeds as follows.    -   The decoding process for reference picture set as specified in        subclause 8.3.2 is invoked.    -   If the current picture is an IDR or a BLA picture, the following        applies:        -   1. When the IDR or BLA picture is not the first picture            decoded and the value of pic_width_in_luma_samples or            pic_height_in_luma_samples or            sps_max_dec_pic_buffering[TargetDecHighestTid] derived from            the active sequence parameter set is different from the            value of pic_width_in_luma_samples or            pic_height_in_luma_samples or            sps_max_dec_pic_buffering[TargetDecHighestTid] derived from            the sequence parameter set that was active for the preceding            picture, respectively, no_output_of_prior_pics_flag is            inferred to be equal to 1 by the HRD, regardless of the            actual value of no_output_of_prior_pics_flag.            -   NOTE—Decoder implementations should try to handle                picture or DPB size changes more gracefully than the HRD                in regard to changes in pic_width_in_luma_samples,                pic_height_in_luma_samples, or                sps_max_dec_pic_buffering[TargetDecHighestTid].        -   2. When no_output_of_prior_pics_flag is equal to 1 or is            inferred to be equal to 1, all picture storage buffers in            the DPB are emptied without output of the pictures they            contain, and DPB fullness is set to 0.    -   All pictures k in the DPB, for which both of the following        conditions are true, are removed from the DPB:        -   picture k is marked as “unused for reference”,        -   picture k has PicOutputFlag equal to 0 or its DPB output            time is less than or equal to the CPB removal time of the            first decoding unit (denoted as decoding unit m) of the            current picture n; i.e. t_(o,dpb)(k)<=t_(r)(m)    -   When a picture is removed from the DPB, the DPB fullness is        decremented by one.

As indicated elsewhere in this disclosure, the parameterssps_max_dec_pic_buffering[i] may not be properly selected in HRDoperations. HEVC Working Draft 8 merely indicatessps_max_dec_pic_buffering[i] instead ofsps_max_dec_pic_buffering[TargetDecHighestTid], as shown above. HEVCWorking Draft 8 does not indicate the semantics of the index i insection C.2.1. Specifying TargetDecHighestTid as the index i ofsps_max_dec_pic_buffering[i] may, in accordance with one or moretechniques of this disclosure, ensure that i equal to theclearly-specified value of TargetDecHighestTid is used insps_max_dec_pic_buffering[i] when performing the HRD operation ofremoving pictures from the DPB.

As shown in the above modifications to section C.2.1 of HEVC WorkingDraft 8, a device may decode, from an SPS active for a current picture,a first array of syntax elements (sps_max_dec_pic_buffering[ ]) thateach indicate a maximum required size of a DPB of the HRD. In addition,the device may decode, from an SPS active for a preceding picture, asecond array of syntax elements (sps_max_dec_pic_buffering[ ]) that eachindicate a maximum required size of the DPB of the HRD. The device maydetermine, based on the target highest temporal identifier(TargetDecHighestTid), a first syntax element in the first array(sps_max_dec_pic_buffering[TargetDecHighestTid]). In addition, thedevice may determine, based on the target highest temporal identifier, asecond syntax element in the second array(sps_max_dec_pic_buffering[TargetDecHighestTid]). When the currentpicture is an instantaneous decoding refresh (IDR) picture or a brokenlink access (BLA) picture and a value of the first syntax element isdifferent than a value of the second syntax element, the device mayinfer a value of a third syntax element (no_output_of_prior_pics_flag)regardless of a value indicated by the third syntax element. The thirdsyntax element may specify how previously-decoded pictures in the DPBare treated after decoding of an IDR picture or BLA picture.

An IDR picture may be a random access point (RAP) picture for which eachslice segment has a nal_unit_type equal to IDR_W_LP or IDR_N_LP. An IDRpicture contains only I slices, and may be the first picture in thebitstream in decoding order, or may appear later in the bitstream. AnIDR picture having nal_unit_type equal to IDR_N_LP does not haveassociated leading pictures present in the bitstream. A leading pictureis a picture that precedes the associated RAP picture in output order.An IDR picture having nal_unit_type equal to IDR_W_LP does not haveassociated tagged-for-discard (TFD) pictures present in the bitstream,but may have associated DLP pictures in the bitstream.

A BLA picture is a RAP picture for which each slice segment hasnal_unit_type equal to BLA_W_TFD, BLA_W_DLP or BLA_N_LP. A BLA picturehaving nal_unit_type equal to BLA_W_TFD may have associated TFD picturespresent in the bitstream. A BLA picture having nal_unit_type equal toBLA_N_LP does not have associated leading pictures present in thebitstream. A BLA picture having nal_unit_type equal to BLA_W_DLP doesnot have associated TFD pictures present in the bitstream, but may haveassociated DLP pictures in the bitstream.

Section C.3 of HEVC Working Draft 8 describes bitstream conformanceoperations. In accordance with one or more example techniques of thisdisclosure, section C.3 of HEVC Working Draft 8 may be modified asfollows:

-   -   A bitstream of coded data conforming to this Specification shall        fulfill all requirements specified in this subclause.    -   The bitstream shall be constructed according to the syntax,        semantics, and constraints specified in this Specification        outside of this annex.    -   The first coded picture in a bitstream shall be a RAP picture,        i.e. an IDR picture, a CRA picture, or a BLA picture.    -   For each current picture that is decoded, let the variables        maxPicOrderCnt and minPicOrderCnt be set equal to the maximum        and the minimum, respectively, of the PicOrderCntVal values of        the following pictures:        -   The current picture.        -   The previous picture in decoding order that has TemporalId            equal to 0.        -   The short-term reference pictures in the reference picture            set of the current picture.        -   All pictures n that have PicOutputFlag equal to 1 and            t_(r)(n)<t_(r)(currPic) and t_(o,dpb)(n)>=t_(r)(currPic),            where currPic is the current picture.    -   All of the following conditions shall be fulfilled for each of        the bitstream conformance tests:        -   1. For each access unit n, with n>0, associated with a            buffering period SEI message, with Δt_(g,90)(n) specified by            Δt _(g,90)(n)=90000*(t _(r,n)(n)−t _(af)(n−1))  (C-18)        -   the value of InitCpbRemovalDelay[SchedSelIdx] shall be            constrained as follows.            -   If cbr_flag[SchedSelIdx] is equal to 0,                InitCpbRemovalDelay[SchedSelIdx]<=Ceil(Δt                _(g,90)(n))  (C-19)            -   Otherwise (cbr_flag[SchedSelIdx] is equal to 1),                Floor(Δt                _(g,90)(n))<=InitCpbRemovalDelay[SchedSelIdx]<=Ceil(Δt                _(g,90)(n))  (C-20)                -   NOTE 4—The exact number of bits in the CPB at the                    removal time of each picture may depend on which                    buffering period SEI message is selected to                    initialize the HRD. Encoders must take this into                    account to ensure that all specified constraints                    must be obeyed regardless of which buffering period                    SEI message is selected to initialize the HRD, as                    the HRD may be initialized at any one of the                    buffering period SEI messages.    -   2. A CPB overflow is specified as the condition in which the        total number of bits in the CPB is larger than the CPB size. The        CPB shall never overflow.    -   3. A CPB underflow is specified as the condition in which the        nominal CPB removal time of decoding unit m t_(r,n)(m) is less        than the final CPB arrival time of decoding unit m t_(af)(m) for        at least one value of m. When low_delay_hrd_flag is equal to 0,        the CPB shall never underflow.    -   4. When low_delay_hrd_flag is equal to 1, a CPB underflow may        occur at decoding unit in m. this case, the final CPB arrival        time of access unit n containing decoding unit m t_(af)(n) shall        be greater than the nominal CPB removal time of access unit n        containing decoding unit m t_(r,n)(n).    -   5. The nominal removal times of pictures from the CPB (starting        from the second picture in decoding order), shall satisfy the        constraints on t_(r,n)(n) and t_(r)(n) expressed in subclauses        A.4.1 through A.4.2.    -   6. For each current picture that is decoded, after invocation of        the process for removal of pictures from the DPB as specified in        subclause C.3.1, the number of decoded pictures in the DPB,        including all pictures n that are marked as “used for reference”        or that have PicOutputFlag equal to 1 and        t_(o,dpb)(n)>=t_(r)(currPic), where currPic is the current        picture, shall be less than or equal to Max(0,        sps_max_dec_pic_buffering[TargetDecHighestTid]−1).    -   7. All reference pictures shall be present in the DPB when        needed for prediction. Each picture that has OutputFlag equal to        1 shall be present in the DPB at its DPB output time unless it        is removed from the DPB before its output time by one of the        processes specified in subclause C.3.    -   8. For each current picture that is decoded, the value of        maxPicOrderCnt−minPicOrderCnt shall be less than        MaxPicOrderCntLsb/2.    -   9. The value of Δ_(to,dpb)(n) as given by Equation C-17, which        is the difference between the output time of a picture and that        of the first picture following it in output order and having        PicOutputFlag equal to 1, shall satisfy the constraint expressed        in subclause A.4.1 for the profile, tier and level specified in        the bitstream using the decoding process specified in clauses        2-9.

As indicated elsewhere in this disclosure, the parameterssps_max_dec_pic_buffering[i] may not be properly selected in bitstreamconformance operations. In item 6 of section C.3, HEVC Working Draft 8indicates that “the number of decoded pictures in the DPB . . . shall beless than or equal to Min(0, sps_max_dec_pic_buffering[TemporalId]−1),”where TemporalId is not defined. Specifying TargetDecHighestTid as theindex i of sps_max_dec_pic_buffering[i] may, in accordance with one ormore techniques of this disclosure, ensure that i equal to theclearly-specified value of TargetDecHighestTid is used insps_max_dec_pic_buffering[i] when performing the bitstream conformanceoperations.

When a device performs a decoding process as part of a HRD operation,the device may decode, from a SPS, an array of syntax elements(sps_max_dec_pic_buffering[ ]), that each indicate a maximum requiredsize of a DPB of the HRD. Furthermore, as part of performing the HRDoperation, the device may determine, based on the target highesttemporal identifier (TargetDecHighestTid), a particular syntax elementin the array. Furthermore, as shown in the above modifications tosection C.3 of HEVC Working Draft 8, the device may determine, based atleast in part on whether a number of decoded pictures in the DPB is lessthan or equal to the maximum of 0 and a value of the particular syntaxelement minus 1, whether the bitstream conforms to the video codingstandard.

Section C.4 of HEVC Working Draft 8 describes decoder conformance. Inaccordance with one or more example techniques of this disclosure,section C.4 of HEVC Working Draft 8 may be changed as follows:

-   -   A decoder conforming to this Specification shall fulfill all        requirements specified in this subclause.    -   A decoder claiming conformance to a specific profile, tier and        level shall be able to successfully decode all bitstreams that        conform to the bitstream conformance requirements specified in        subclause C.4, in the manner specified in Annex A, provided that        all video parameter sets, sequence parameter sets, and picture        parameter sets referred to in the VCL NAL units, and appropriate        buffering period and picture timing SEI messages are conveyed to        the decoder, in a timely manner, either in the bitstream (by        non-VCL NAL units), or by external means not specified by this        Specification.    -   When a bitstream contains syntax elements that have values that        are specified as reserved and it is specified that decoders        shall ignore values of the syntax elements or NAL units        containing the syntax elements having the reserved values, and        the bitstream is otherwise conforming to this Specification, a        conforming decoder shall decode the bitstream in the same manner        as it would decode a conforming bitstream and ignore values of        the syntax elements or NAL units containing the syntax elements        having the reserved values as specified.    -   There are two types of conformance that can be claimed by a        decoder: output timing conformance and output order conformance.    -   To check conformance of a decoder, test bitstreams conforming to        the claimed profile, tier and level, as specified by subclause        C.4 are delivered by a hypothetical stream scheduler (HSS) both        to the HRD and to the decoder under test (DUT). All pictures        output by the HRD shall also be output by the DUT and, for each        picture output by the HRD, the values of all samples that are        output by the DUT for the corresponding picture shall be equal        to the values of the samples output by the HRD.    -   For output timing decoder conformance, the HSS operates as        described above, with delivery schedules selected only from the        subset of values of SchedSelIdx for which the bit rate and CPB        size are restricted as specified in Annex A for the specified        profile, tier and level, or with “interpolated” delivery        schedules as specified below for which the bit rate and CPB size        are restricted as specified in Annex A. The same delivery        schedule is used for both the HRD and DUT.    -   When the HRD parameters and the buffering period SEI messages        are present with cpb_cnt_minus1[TargetDecHighestTid] greater        than 0, the decoder shall be capable of decoding the bitstream        as delivered from the HSS operating using an “interpolated”        delivery schedule specified as having peak bit rate r, CPB size        c(r), and initial CPB removal delay (f(r)÷r) as follows:        α=(r−BitRate[SchedSelIdx−1])÷(BitRate[SchedSelIdx]−BitRate[SchedSelIdx−1]),  (C-22)        c(r)=α*CpbSize[SchedSelIdx]+(1−α)*CpbSize[SchedSelIdx−1],  (C-23)        f(r)=α*InitCpbRemovalDelay[SchedSelIdx]*BitRate[SchedSelIdx]+(1−α)*InitCpbRemovalDelay[SchedSelIdx−1]*BitRate[SchedSelIdx−1]  (C-24)    -   for any SchedSelIdx>0 and r such that        BitRate[SchedSelIdx−1]<=r<=BitRate[SchedSelIdx] such that r and        c(r) are within the limits as specified in Annex A for the        maximum bit rate and buffer size for the specified profile, tier        and level.        -   NOTE 1—InitCpbRemovalDelay[SchedSelIdx] can be different            from one buffering period to another and have to be            re-calculated.    -   For output timing decoder conformance, an HRD as described above        is used and the timing (relative to the delivery time of the        first bit) of picture output is the same for both HRD and the        DUT up to a fixed delay.    -   For output order decoder conformance, the following applies.        -   The HSS delivers the bitstream BitstreamToDecode to the DUT            “by demand” from the DUT, meaning that the HSS delivers bits            (in decoding order) only when the DUT requires more bits to            proceed with its processing.        -   NOTE 2—This means that for this test, the coded picture            buffer of the DUT could be as small as the size of the            largest decoding unit.        -   A modified HRD as described below is used, and the HSS            delivers the bitstream to the HRD by one of the schedules            specified in the bitstream BitstreamToDecode such that the            bit rate and CPB size are restricted as specified in            Annex A. The order of pictures output shall be the same for            both HRD and the DUT.        -   For output order decoder conformance, the CPB size is            CpbSize[SchedSelIdx] as specified by Equation E-46, where            SchedSelIdx and the HRD parameters are selected as specified            above in subclause C.1. The DPB size is            sps_max_dec_pic_buffering[TargetDecHighestTid]. Removal time            from the CPB for the HRD is equal to final bit arrival time            and decoding is immediate. The operation of the DPB of this            HRD is as described in subclauses C.5.1 through C.5.3.

As indicated elsewhere in this disclosure, the parameterscpb_cnt_minus1[i] and sps_max_dec_pic_buffering[i] may not be properlyselected in decoder conformance requirements. For instance, section C.4of HEVC Working Draft 8 does not specify an index for cpb_cnt_minus1.Specifying TargetDecHighestTid as the index i of cpb_cnt_minus1[i] andsps_max_dec_pic_buffering[i] may, in accordance with one or moretechniques of this disclosure, ensure that decoder conformanceoperations are consistently performed with i equal to theclearly-specified value of TargetDecHighestTid.

Furthermore, section C.4.2 of HEVC Working Draft 8 describes removal ofpictures from the DPB for decoder conformance. In accordance with one ormore example techniques of this disclosure, the title of section C.4.2may be changed from “removal of pictures from the DPB” to “output andremoval of pictures from the DPB.” The text of section C.4.2 of HEVCWorking Draft 8 may be changed as follows:

-   -   The output and removal of pictures from the DPB before decoding        of the current picture (but after parsing the slice header of        the first slice of the current picture) happens instantaneously        when the first decoding unit of the access unit containing the        current picture is removed from the CPB and proceeds as follows.    -   The decoding process for reference picture set as specified in        subclause 8.3.2 is invoked.        -   If the current picture is an IDR or a BLA picture, the            following applies.            -   1. When the IDR or BLA picture is not the first picture                decoded and the value of pic_width_in_luma_samples or                pic_height_in_luma_samples or                sps_max_dec_pic_buffering[TargetDecHighestTid] derived                from the active sequence parameter set is different from                the value of pic_width_in_luma_samples or                pic_height_in_luma_samples or                sps_max_dec_pic_buffering[TargetDecHighestTid] derived                from the sequence parameter set that was active for the                preceding picture, respectively,                no_output_of_prior_pics_flag is inferred to be equal to                1 by the HRD, regardless of the actual value of                no_output_of_prior_pics_flag.                -   NOTE—Decoder implementations should try to handle                    picture or DPB size changes more gracefully than the                    HRD in regard to changes in                    pic_width_in_luma_samples,                    pic_height_in_luma_samples or                    sps_max_dec_pic_buffering[TargetDecHighestTid].            -   2. When no_output_of_prior_pics_flag is equal to 1 or is                inferred to be equal to 1, all picture storage buffers                in the DPB are emptied without output of the pictures                they contain.            -   3. When no_output_of_prior_pics_flag is not equal to 1                and is not inferred to be equal to 1, picture storage                buffers containing a picture that is marked as “not                needed for output” and “unused for reference” are                emptied (without output), and all non-empty picture                storage buffers in the DPB are emptied by repeatedly                invoking the “bumping” process specified in subclause                C.5.2.1.        -   Otherwise (the current picture is not an IDR or a BLA            picture), picture storage buffers containing a picture which            are marked as “not needed for output” and “unused for            reference” are emptied (without output). When one or more of            the following conditions are true, the “bumping” process            specified in subclause C.5.2.1 is invoked repeatedly until            there is an empty picture storage buffer to store the            current decoded picture.            -   1. The number of pictures in the DPB that are marked as                “needed for output” is greater than                sps_max_num_reorder_pics[TargetDecHighestTid].            -   2. The number of pictures in the DPB is equal to                sps_max_dec_pic_buffering[TargetDecHighestTid].

“Bumping” Process

The “bumping” process is invoked in the following cases.

-   -   The current picture is an IDR or a BLA picture and        no_output_of_prior_pics_flag is not equal to 1 and is not        inferred to be equal to 1, as specified in subclause C.5.2.    -   The current picture is not an IDR or a BLA picture, and the        number of pictures in the DPB that are marked “needed for        output” is greater than        sps_max_num_reorder_pics[TargetDecHighestTid], as specified in        subclause C.5.2.    -   The current picture is not an IDR or a BLA picture and the        number of pictures in the DPB is equal to        sps_max_dec_pic_buffering[TargetDecHighestTid], as specified in        subclause C.5.2.

The “bumping” process consists of the following ordered steps:

-   -   1. The picture that is first for output is selected as the one        having the smallest value of PicOrderCntVal of all pictures in        the DPB marked as “needed for output”.    -   2. The picture is cropped, using the cropping rectangle        specified in the active sequence parameter set for the picture,        the cropped picture is output, and the picture is marked as “not        needed for output”.    -   3. If the picture storage buffer that included the picture that        was cropped and output contains a picture marked as “unused for        reference”, the picture storage buffer is emptied.

As indicated elsewhere in this disclosure, the parameterssps_max_dec_pic_buffering[i] and sps_max_num_reorder_pics[i] may not beproperly selected in HRD operations, such as removal of pictures fromthe DPB. Specifying TargetDecHighestTid as the index i ofsps_max_dec_pic_buffering[i] and sps_max_num_reorder_pics[i] may, inaccordance with one or more techniques of this disclosure, ensure that iequal to the clearly-specified value of TargetDecHighestTid is used insps_max_dec_pic_buffering[i] and sps_max_num_reorder_pics[i] whenperforming the HRD operation of removing pictures from the DPB.

When a device performs a decoding process during an HRD operation, thedevice may decode, from a SPS, an array of syntax elements(sps_max_dec_pic_buffering[ ]) that each indicate a maximum requiredsize of a DPB of the HRD. Furthermore, when the device performs the HRDoperation, the device may determine, based on the target highesttemporal identifier, a particular syntax element in the array(sps_max_dec_pic_buffering[TargetDecHighestTid]). Furthermore, thedevice may perform a bumping process that empties one or more picturestorage buffers of the DPB when a current picture is not an IDR pictureor a BLA picture and the number of pictures in the DPB marked as neededfor output is greater than a value of the particular syntax element.

Similarly, when a device performs a decoding process during an HRDoperation, the device may decode, from a SPS, an array of syntaxelements (sps_max_dec_pic_buffering[ ]) that each indicate a maximumrequired size of a DPB of the HRD. Furthermore, when the device performsthe HRD operation, the device may determine, based on the target highesttemporal identifier, a particular syntax element in the array(sps_max_dec_pic_buffering[TargetDecHighestTid]). Furthermore, thedevice may perform a bumping process that empties one or more picturestorage buffers of the DPB when a current picture is not an IDR pictureor a BLA picture and the number of pictures in the DPB is equalindicated by the particular syntax element.

Furthermore, in accordance with one or more techniques of thisdisclosure, an applicable_operation_points( ) syntax structure andassociated semantics may be added to HEVC Working Draft 8. Table 5,below, shows an example syntax of the applicable_operation_points( )syntax structure.

TABLE 5 Applicable Operation Points applicable_operation_points( ) { num_applicable_ops_minus1 ue(v)  if( num_applicable_ops_minus1 > 0)  default_op_applicable_flag u(1)  mumOpsSignalled =default_op_applicable_flag ?      num_applicable_ops_minus1 :     num_applicable_ops_minus1 + 1  for( i = 0; i < mumOpsSignalled; i++) {   operation_point_layer_ids( i )   op_temporal_id[ i ] u(3)  } }

The applicable_operation_point( ) syntax structure shown in Table 5specifies the operation points to which the SEI message associated withthis syntax structure applies. The SEI message associated with anapplicable_operation_point( ) syntax structure (also referred to as theassociated SEI message) is the SEI message that contains theapplicable_operation_point( ) syntax structure. The SEI messageassociated with an applicable_operation_point( ) syntax structure may bea buffering period SEI message, a picture timing SEI message or asub-picture timing SEI message.

A default operation point may be defined as the operation pointidentified by OpLayerIdSet containing values 0 to nuh_reserved_zero_(—)6bits, inclusive, where nuh_reserved_zero_(—)6 bits is coded in the NALunit header of the SEI NAL unit containing the associated SEI message,and OpTid is equal to the TemporalId value of the SEI NAL unitcontaining the associated SEI message. Alternatively, the defaultoperation point may be defined as the operation point identified by theOpLayerIdSet containing only the nuh_reserved_zero_(—)6 bits in the NALunit header of the SEI NAL unit containing the associated SEI message,and OpTid is equal to the TemporalId value of the SEI NAL unitcontaining the associated SEI message. Alternatively, the defaultoperation point may be defined as the operation point identified by theOpLayerIdSet containing only the value 0, and OpTid is equal to theTemporalId value of the SEI NAL unit containing the associated SEImessage.

If default_op_applicable_flag is equal to 1, the operation points towhich the associated SEI message applies are the default operation pointand the num_applicable_ops_minus1 operation points identified byOpLayerIdSet as specified by operation_point_layer_ids(i) and OpTidequal to op temporal_id[i], with i in the range of 0 tonum_applicable_ops_minus1, inclusive. Otherwise(default_op_applicable_flag is equal to 0), the operation points towhich the associated SEI message applies may be thenum_applicable_ops_minus1+1 operation points identified by OpLayerIdSetas specified by operation_point_layer_ids(i) and OpTid equal to optemporal_id[i], with i in the range of 0 to num_applicable_ops_minus1+1,inclusive.

Furthermore, in the example syntax of Table 5, thenum_applicable_ops_minus1 syntax element, plus 1, specifies the numberof operation points to which the associated SEI message applies. Thevalue of num_applicable_ops_minus1 may be in the range of 0 to 63,inclusive. In the example of Table 5, the default_op_applicable_flagsyntax element equal to 1 specifies that the associated SEI messageapplies to the default operation point. The default_op_applicable_flagsyntax element equal to 0 specifies that the associated SEI message doesnot apply to the default operation point. The op temporal_id[i] syntaxelement specifies the i-th OpTid value explicitly signaled in theapplicable_operation_point( ) syntax structure. The value of optemporal_id[i] may be in the range of 0 to 6, inclusive.

As indicated above, HEVC Working Draft 8 provides no way to associate abuffering period SEI message or picture timing SEI message to ahrd_parameters( ) syntax structure for which the associatedoperation_point_layer_ids( ) syntax structure includes multiple valuesof nuh_reserved_zero_(—)6 bits (i.e., multiple layer IDs in a multiview,3DV or scalable video coding extension of HEVC). The inclusion of theapplicable_operation_point( ) syntax structure may at least partiallyresolve this problem. The applicable_operation_point( ) syntax structuremay clearly specify the operation points to which a buffering period SEImessage, a picture timing SEI message or a sub-picture timing SEImessage applies. This may allow the use of information carried in thesyntax elements nuh_reserved_zero_(—)6 bits and temporal_id_plus1 in theNAL unit header of SEI NAL units, and may allow the sharing of theinformation conveyed in a same buffering period, picture timing orsub-picture timing SEI message for processing of video data associatedwith multiple operation points.

Section D.1.1 of HEVC Working Draft 8 describes the syntax of bufferingperiod SEI messages. In accordance with one or more example techniquesof this disclosure, the buffering period SEI message syntax may bechanged as shown in Table 6, below. The changes to the buffering periodSEI message syntax may enable buffering period SEI messages to includeapplicable_operation_points( ) syntax structures.

TABLE 6 Buffering Period De- scrip- Buffering_period( payloadSize ) {tor  seq_parameter_set_id ue(v)  applicable_operation_points( )  if(!sub_pic_cpb_params_present_flag )   rap_cpb_params_present_flag u(1) if( NalHrdBpPresentFlag ) {   for( SchedSelIdx = 0; SchedSelIdx <CpbCnt;   SchedSelIdx++ ) {    initial_cpb_removal_delay[ SchedSelIdx ]u(v)    initial_cpb_removal_delay_offset[ SchedSelIdx ] u(v)    if(sub_pic_cpb_params_present_flag ||     rap_cpb_params_present_flag ) {    initial_alt_cpb_removal_delay[ SchedSelIdx ] u(v)    initial_alt_cpb_removal_delay_offset[ SchedSelIdx ] u(v)    }   }  } if( VclHrdBpPresentFlag ) {   for( SchedSelIdx = 0; SchedSelIdx <CpbCnt;   SchedSelIdx++ ) {    initial_cpb_removal_delay[ SchedSelIdx ]u(v)    initial_cpb_removal_delay_offset[ SchedSelIdx ] u(v)    if(sub_pic_cpb_params_present_flag ||     rap_cpb_params_present_flag) {    initial_alt_cpb_removal_delay[ SchedSelIdx ] u(v)    initial_alt_cpb_removal_delay_offset[ SchedSelIdx ] u(v)    }   }  }}

Section D.2.1 of HEVC Working Draft 8 describes the semantics of thesyntax elements of buffering period SEI messages. In accordance with oneor more techniques of this disclosure, the semantics of thebuffering_period(payloadSize) syntax structure may be changed asfollows. Semantics for those syntax elements not mentioned are the sameas in HEVC Working Draft 8.

-   -   A buffering period SEI message provides information of initial        CPB removal delay and initial CPB removal_delay_offset.    -   The following applies for the buffering period SEI message        syntax and semantics:        -   The syntax elements initial_cpb_removal_delay_length_minus1            and sub_pic_cpb_params_present_flag, and the variables            NalHrdBpPresentFlag, VclHrdBpPresentFlag,            CpbSize[SchedSelIdx], BitRate[SchedSelIdx], and CpbCnt are            found in or derived from syntax elements found in the            hrd_parameters( ) syntax structure and the            sub_layer_hrd_parameters( ) syntax structure applicable to            any of the operation points that the buffering period SEI            message applies to.        -   Any two operation points that the buffering period SEI            message applies to having different OpTid values tIdA and            tIdB indicates that the values of cpb_cnt_minus1[tIdA] and            cpb_cnt_minus1[tIdB] coded in the hrd_parameters( ) syntax            structure(s) applicable to the two operation points are            identical.        -   Any two operation points that the buffering period SEI            message applies to having different OpLayerIdSet values            layerIdSetA and layerIdSetB indicates that the values of            nal_hrd_parameters_present_flag and            vcl_hrd_parameters_present_flag, respectively, for the two            hrd_parameters( ) syntax structures applicable to the two            operation points are identical.        -   The bitstream (or a part thereof) refers to the bitstream            subset (or a part thereof) associated with any of the            operation points the buffering period SEI message applies            to.    -   If NalHrdBpPresentFlag or VclHrdBpPresentFlag are equal to 1, a        buffering period SEI message applicable to the specified        operation points may be present in any access unit in the coded        video sequence, and a buffering period SEI message applicable to        the specified operation points shall be present in each RAP        access unit, and in each access unit associated with a recovery        point SEI message. Otherwise (NalHrdBpPresentFlag and        VclHrdBpPresentFlag are both equal to 0), no access unit in the        coded video sequence shall have a buffering period SEI message        applicable to the specified operation points.        -   NOTE—For some applications, frequent presence of a buffering            period SEI message may be desirable.    -   When an SEI NAL unit that contains a buffering period SEI        message and has nuh_reserved_zero_(—)6 bits equal to 0 is        present, the SEI NAL unit shall precede, in decoding order, the        first VCL NAL unit in the access unit.    -   A buffering period is specified as the set of access units        between two instances of the buffering period SEI message        consecutive in decoding order.    -   The variable CpbCnt is derived to be equal to        cpb_cnt_minus1[tId]+1, where cpb_cnt_minus1[tId] is coded in the        hrd_parameters( ) syntax structure that is applicable to any of        the operation points that the buffering period SEI message        applies to and that have OpTid equal to tId.    -   seq_parameter_set_id refers to the active sequence parameter        set. The value of seq_parameter_set_id shall be equal to the        value of seq_parameter_set_id in the picture parameter set        referenced by the coded picture associated with the buffering        period SEI message. The value of seq_parameter_set_id shall be        in the range of 0 to 31, inclusive.    -   rap_cpb_params_present_flag equal to 1 specifies the presence of        the initial_alt_cpb_removal_delay[SchedSelIdx] and        initial_alt_cpb_removal_delay_offset[SchedSelIdx] syntax        elements. When not present, the value of        alt_cpb_params_present_flag is inferred to be equal to 0. When        the associated picture is neither a CRA picture nor a BLA        picture, the value of alt_cpb_params_present_flag shall be equal        to 0.    -   initial_cpb_removal_delay[SchedSelIdx] and    -   initial_alt_cpb_removal_delay[SchedSelIdx] specify the default        and the alternative initial CPB removal delays, respectively,        for the SchedSelIdx-th CPB. The syntax elements have a length in        bits given by initial_cpb_removal_delay_length_minus1+1, and are        in units of a 90 kHz clock. The values of the syntax elements        shall not be equal to 0 and shall be less than or equal to        90000*(CpbSize[SchedSelIdx]÷BitRate[SchedSelIdx]), the        time-equivalent of the CPB size in 90 kHz clock units.    -   initial_cpb_removal_delay_offset[SchedSelIdx] and    -   initial_alt_cpb_removal_delay_offset[SchedSelIdx] specify the        default and the alternative initial CPB removal offsets,        respectively, for the SchedSelIdx-th CPB. The syntax elements        have a length in bits given by        initial_cpb_removal_delay_length_minus1+1 and are in units of a        90 kHz clock. These syntax elements are not used by decoders and        may be needed only for the delivery scheduler (HSS) specified in        Annex C.

The buffering period SEI message may include HRD parameters (e.g.,initial_cpb_removal delay[SchedSelIdx],initial_cpb_removal_delay_offset[SchedSelIdx],initial_alt_cpb_removal_delay[SchedSelIdx] andinitial_alt_cpb_removal_delay_offset[SchedSelIdx]). As indicated above,HEVC Working Draft 8 provides no way to associate a buffering period SEImessage to a hrd_parameters( ) syntax structure in a VPS for which theassociated operation_point_layer_ids( ) syntax structure includesmultiple values of nuh_reserved_zero_(—)6 bits (i.e. multiple layer IDsin a multiview, 3DV or scalable video coding extension of HEVC). Hence,in accordance with one or more techniques of this disclosure, theapplicable_operation_points( ) syntax element in the buffering periodSEI message specifies the operation points to which the buffering periodSEI message applies.

Section D.1.2 of HEVC Working Draft 8 indicates the syntax of picturetiming SEI messages. In accordance with one or more techniques of thisdisclosure, the syntax of the picture timing SEI message may be changedas shown in Table 7, below. The changes to the picture timing SEImessage syntax may enable picture timing SEI messages to includeapplicable_operation_points( ) syntax structures.

TABLE 7 Picture Timing SEI Message pic_timing( payloadSize ) {Descriptor  applicable_operation_points( )  au_cpb_removal_delay_minus1u(v)  pic_dpb_output_delay u(v)  if( sub_pic_cpb_params_present_flag ) {  num_decoding_units_minus1 ue(v)   du_common_cpb_removal_delay_flagu(1)   if( du_common_cpb_removal_delay_flag )   du_common_cpb_removal_delay_minus1 u(v)   for( i = 0; i <=num_decoding_units_minus1; i++ ) {    num_nalus_in_du_minus1[ i ] ue(v)   if( !du_common_cpb_removal_delay_flag )    du_cpb_removal_delay_minus1[ i ] u(v)   }  } }

In addition, the semantics of the picture timing SEI message may bechanged as follows. Semantics for those syntax elements of thepic_timing(payloadSize) syntax structure not mentioned below may be thesame as those in HEVC Working Draft 8.

-   -   The picture timing SEI message provides information of CPB        removal delay and DPB output delay for the access unit        associated with the SEI message.    -   The following applies for the picture timing SEI message syntax        and semantics:        -   The syntax elements sub_pic_cpb_params_present_flag,            cpb_removal_delay_length_minus1,            dpb_output_delay_length_minus1, and            du_cpb_removal_delay_length_minus1, and the variable            CpbDpbDelaysPresentFlag are found in or derived from syntax            elements found in the hrd_parameters( ) syntax structure and            the sub_layer_hrd_parameters( ) syntax structure applicable            to any of the operation points that the picture timing SEI            message applies to.        -   The bitstream (or a part thereof) refers to the bitstream            subset (or a part thereof) associated with any of the            operation points the picture timing SEI message applies to.        -   NOTE 1—The syntax of the picture timing SEI message is            dependent on the content of the hrd_parameters( ) syntax            structures applicable to the operation points the picture            timing SEI message applies to. These hrd_parameters( )            syntax structures are in the video parameter set and/or the            sequence parameter set that are active for the coded picture            associated with the picture timing SEI message. When the            picture timing SEI message is associated with a CRA access            unit that is the first access unit in the bitstream, an IDR            access unit, or a BLA access unit, unless it is preceded by            a buffering period SEI message within the same access unit,            the activation of the video parameter set and sequence            parameter set (and, for IDR or BLA pictures that are not the            first picture in the bitstream, the determination that the            coded picture is an IDR picture or a BLA picture) does not            occur until the decoding of the first coded slice NAL unit            of the coded picture. Since the coded slice NAL unit of the            coded picture follows the picture timing SEI message in NAL            unit order, there may be cases in which it is necessary for            a decoder to store the RBSP containing the picture timing            SEI message until determining the active video parameter set            and/or the active sequence parameter set, and then perform            the parsing of the picture timing SEI message.    -   The presence of picture timing SEI message in the bitstream is        specified as follows.        -   If CpbDpbDelaysPresentFlag is equal to 1, one picture timing            SEI message applicable to the specified operation points            shall be present in every access unit of the coded video            sequence.        -   Otherwise (CpbDpbDelaysPresentFlag is equal to 0), no            picture timing SEI messages applicable to the specified            operation points shall be present in any access unit of the            coded video sequence.

When an SEI NAL unit that contains a picture timing SEI message and hasnuh_reserved_zero_(—)6 bits equal to 0 is present, the SEI NAL unitshall precede, in decoding order, the first VCL NAL unit in the accessunit.

-   -   au_cpb_removal_delay_minus1 plus 1 specifies, when the HRD        operates at access unit level, how many clock ticks to wait        after removal from the CPB of the access unit associated with        the most recent buffering period SEI message in a preceding        access unit before removing from the buffer the access unit data        associated with the picture timing SEI message. This value is        also used to calculate an earliest possible time of arrival of        access unit data into the CPB for the HSS. The syntax element is        a fixed length code whose length in bits is given by        cpb_removal_delay_length_minus1+1.        -   NOTE 2—The value of cpb_removal_delay_length_minus1 that            determines the length (in bits) of the syntax element            au_cpb_removal_delay_minus1 is the value of            cpb_removal_delay_length_minus1 coded in the video parameter            set or the sequence parameter set that is active for the            coded picture associated with the picture timing SEI            message, although au_cpb_removal_delay_minus1 plus 1            specifies a number of clock ticks relative to the removal            time of the preceding access unit containing a buffering            period SEI message, which may be an access unit of a            different coded video sequence.    -   pic_dpb_output_delay is used to compute the DPB output time of        the picture. It specifies how many clock ticks to wait after        removal of the last decoding unit in an access unit from the CPB        before the decoded picture is output from the DPB.        -   NOTE 3—A picture is not removed from the DPB at its output            time when it is still marked as “used for short-term            reference” or “used for long-term reference”.        -   NOTE 4—Only one pic_dpb_output_delay is specified for a            decoded picture.    -   The length of the syntax element pic_dpb_output_delay is given        in bits by dpb_output_delay_length_minus1+1. When        sps_max_dec_pic_buffering[minTid] is equal to 1, where minTid is        the minimum of the OpTid values of all operation points the        picture timing SEI message applies to, pic_dpb_output_delay        shall be equal to 0.    -   The output time derived from the pic_dpb_output_delay of any        picture that is output from an output timing conforming decoder        shall precede the output time derived from the        pic_dpb_output_delay of all pictures in any subsequent coded        video sequence in decoding order.    -   The picture output order established by the values of this        syntax element shall be the same order as established by the        values of PicOrderCntVal.    -   For pictures that are not output by the “bumping” process        because they precede, in decoding order, an IDR or BLA picture        with no_output_of_prior_pics_flag equal to 1 or inferred to be        equal to 1, the output times derived from pic_dpb_output_delay        shall be increasing with increasing value of PicOrderCntVal        relative to all pictures within the same coded video sequence.    -   du_common_cpb_removal_delay_flag equal to 1 specifies that the        syntax element du_common_cpb_removal_delay_minus1 is present.        du_common_cpb_removal_delay_flag equal to 0 specifies that the        syntax element du_common_cpb_removal_delay_minus1 is not        present.    -   du_common_cpb_removal_delay_minus1 plus 1 specifies how many        sub-picture clock ticks (see subclause E.2.1) to wait, before        removal from the CPB of each decoding unit in the access unit        associated with the picture timing SEI message, after removal        from the CPB of the previous decoding unit in decoding order.        This value is also used to calculate an earliest possible time        of arrival of decoding unit data into the CPB for the HSS, as        specified in Annex C. The syntax element is a fixed length code        whose length in bits is given by        du_cpb_removal_delay_length_minus1+1.

As indicated above, HEVC Working Draft 8 provides no way to associate apicture timing SEI message to a hrd_parameters( ) syntax structure in aVPS for which the associated operation_point_layer_ids( ) syntaxstructure includes multiple values of nuh_reserved_zero_(—)6 bits (i.e.multiple layer IDs in a multiview, 3DV or scalable video codingextension of HEVC). Hence, in accordance with one or more techniques ofthis disclosure, the applicable_operation_points( ) syntax element inthe picture timing SEI message specifies the operation points to whichthe buffering period SEI message applies.

Furthermore, in accordance with one or more techniques of thisdisclosure, the syntax of the sub-picture timing SEI message may bechanged as shown in Table 8, below. The changes to the sub-picturetiming SEI message syntax may enable sub-picture timing SEI messages toinclude applicable_operation_points( ) syntax structures. In HEVCWorking Draft 8, sub-picture timing SEI message do not include theapplicable_operation_points( ) syntax structure.

TABLE 8 Sub-Picture Timing SEI Message sub_pic_timing( payloadSize ) {Descriptor  applicable_operation_points( ) du_spt_cpb_removal_delay_minus1 u(v) }

Section D.2.2.2 of HEVC Working Draft 8 describes the semantics ofsub-picture timing SEI messages. In accordance with one or moretechniques of this disclosure, section D.2.2.2 of HEVC Working Draft 8may be modified as follows:

-   -   The sub-picture timing SEI message provides CPB removal delay        information for the decoding unit associated with the SEI        message.    -   The following applies for the sub picture timing SEI message        syntax and semantics:        -   The syntax elements sub_pic_cpb_params_present_flag and            cpb_removal_delay_length_minus1, and the variable            CpbDpbDelaysPresentFlag are found in or derived from syntax            elements found in the hrd_parameters( ) syntax structure and            the sub_layer_hrd_parameters( ) syntax structure applicable            to any of the operation points that the sub-picture timing            SEI message applies to.        -   The bitstream (or a part thereof) refers to the bitstream            subset (or a part thereof) associated with any of the            operation points the sub picture timing SEI message applies            to.    -   The presence of the sub-picture timing SEI message in the        bitstream is specified as follows.        -   If CpbDpbDelaysPresentFlag is equal to 1 and            sub_pic_cpb_params_present_flag is equal to 1, one            sub-picture timing SEI message applicable to the specified            operation points may be present in each decoding unit in the            coded video sequence.        -   Otherwise (CpbDpbDelaysPresentFlag is equal to 0 or            sub_pic_cpb_params_present_flag is equal to 0), no            sub-picture timing SEI messages applicable to the specified            operation points shall be present in the coded video            sequence.    -   The decoding unit associated with a sub-picture timing SEI        message consists, in decoding order, of the SEI NAL unit        containing the sub-picture timing SEI message, followed by one        or more NAL units that do not contain a sub-picture timing SEI        message, including all subsequent NAL units in the access unit        up to but not including any subsequent SEI NAL unit containing a        sub-picture timing SEI message. There shall be at least one VCL        NAL unit in each decoding unit. All non-VCL NAL units associated        with a VCL NAL unit shall be included in the same decoding unit.    -   du_spt_cpb_removal_delay_minus 1 plus1 specifies how many        sub-picture clock ticks to wait after removal from the CPB of        the last decoding unit in the access unit associated with the        most recent buffering period SEI message in a preceding access        unit before removing from the CPB the decoding unit associated        with the sub-picture timing SEI message. This value is also used        to calculate an earliest possible time of arrival of decoding        unit data into the CPB for the HSS, as specified in Annex C. The        syntax element is represented by a fixed length code whose        length in bits is given by cpb_removal_delay_length_minus1+1.        -   NOTE—The value of cpb_removal_delay_length_minus1 that            determines the length (in bits) of the syntax element            du_spt_cpb_removal_delay_minus1 is the value of            cpb_removal_delay_length_minus1 coded in the video parameter            set or the sequence parameter set that is active for the            access unit containing the decoding unit associated with the            sub-picture timing SEI message, although            du_spt_cpb_removal_delay_minus1 plus 1 specifies a number of            sub-picture clock ticks relative to the removal time of the            last decoding unit in the preceding access unit containing a            buffering period SEI message, which may be an access unit of            a different coded video sequence.

Section E.2.2 of HEVC Working Draft 8 describes HRD parameter semantics.In accordance with one or more techniques of this disclosure, sectionE.2.2 of HEVC Working Draft 8 may be changed as follows. Semantics forthose syntax elements of HRD parameters not mentioned below may be thesame as those in HEVC Working Draft 8.

-   -   The hrd_parameters( ) syntax structure provides HRD parameters        used in the HRD operations. When the hrd_parameters( ) syntax        structure is included in a video parameter set, the set of        number of nuh_reserved_zero_(—)6 bits values included in the        OpLayerIdSet of the operation points to which the syntax        structure applies is either specified by the corresponding        operation_point_layer_ids( ) syntax structure in the video        parameter set or implicitly derived, as specified in subclause        7.4.4. When the hrd_parameters( ) syntax structure is included        in a sequence parameter set, the applicable operation points are        all the operation points with OpLayerIdSet containing only the        value 0. Alternatively, when the hrd_parameters( ) syntax        structure is included in a sequence parameter set, the        applicable_operation points are all the operation points with        OpLayerIdSet identical to TargetDecLayerIdSet.    -   It is a requirement of bitstream conformance that for all the        hrd_parameters( ) syntax structure in the coded video sequence        (either in the video parameter set or the sequence parameter        set), there shall not be more than one of them that applies to        the same operation point. Alternatively, it is required that        there shall not be more than one hrd_parameters( ) syntax        structure in a video parameter set that applies to the same        operation point. Alternatively, it is required that a video        parameter set shall not include a hrd_parameters( ) syntax        structure that applies to operation points with OpLayerIdSet        containing only the value 0.    -   du_cpb_removal_delay_length_minus1 plus 1 specifies the length,        in bits, of the du_cpb_removal_delay_minus1[i] and        du_common_cpb_removal_delay_minus1 syntax elements of the        picture timing SEI message.    -   cpb_removal_delay_length_minus1 plus 1 specifies the length, in        bits, of the au_cpb_removal_delay_minus1 syntax element in the        picture timing SEI message and the        du_spt_cpb_removal_delay_minus1 syntax element in the        sub-picture timing SEI message. When the        cpb_removal_delay_length_minus1 syntax element is not present,        it is inferred to be equal to 23.    -   dpb_output_delay_length_minus1 plus 1 specifies the length, in        bits, of the pic_dpb_output_delay syntax element in the picture        timing SEI message. When the dpb_output_delay_length_minus1        syntax element is not present, it is inferred to be equal to 23.    -   fixed_pic_rate_flag[i] equal to 1 indicates that, when        TargetDecHighestTid is equal to i, the temporal distance between        the HRD output times of any two consecutive pictures in output        order is constrained as follows.    -   fixed_pic_rate_flag[i] equal to 0 indicates that no such        constraints apply to the temporal distance between the HRD        output times of any two consecutive pictures in output order.    -   When fixed_pic_rate_flag[i] is not present, it is inferred to be        equal to 0. When TargetDecHighestTid is equal to i and        fixed_pic_rate_flag[i] is equal to 1 for a coded video sequence        containing picture n, the value computed for Δt_(o,dpb)(n) as        specified in Equation C-17 shall be equal to        t_(c)*(pic_duration_in_tcs_minus1[i]+1), wherein t_(c) is as        specified in Equation C-1 (using the value of t_(c) for the        coded video sequence containing picture n) when one or more of        the following conditions are true for the following picture nn        that is specified for use in Equation C-17:        -   picture nn is in the same coded video sequence as picture n.        -   picture nn is in a different coded video sequence and            fixed_pic_rate_flag[i] is equal to 1 in the coded video            sequence containing picture nn, the value of            num_units_in_tick÷time_scale is the same for both coded            video sequences, and the value of            pic_duration_in_tc_minus1[i] is the same for both coded            video sequences.    -   pic_duration_in_tc_minus1[i] plus 1 specifies, when        TargetDecHighestTid is equal to i, the temporal distance, in        clock ticks, between the HRD output times of any two consecutive        pictures in output order in the coded video sequence. The value        of pic_duration_in_tc_minus1[i] shall be in the range of 0 to        2047, inclusive.    -   low_delay_hrd_flag[i] specifies the HRD operational mode, when        TargetDecHighestTid is equal to i, as specified in Annex C. When        fixed_pic_rate_flag[i] is equal to 1, low_delay_hrd_flag[i]        shall be equal to 0.        -   NOTE 3—When low_delay_hrd_flag[i] is equal to 1, “big            pictures” that violate the nominal CPB removal times due to            the number of bits used by an access unit are permitted. It            is expected, but not required, that such “big pictures”            occur only occasionally.    -   cpb_cnt_minus1[i] plus 1 specifies the number of alternative CPB        specifications in the bitstream of the coded video sequence when        TargetDecHighestTid is equal to i. The value of        cpb_cnt_minus1[i] shall be in the range of 0 to 31, inclusive.        When low_delay_hrd_flag[i] is equal to 1, cpb_cnt_minus1[i]        shall be equal to 0. When cpb_cnt_minus1[i] is not present, it        is inferred to be equal to 0.

As described elsewhere in this disclosure, in HEVC Working Draft 8, onlythe hrd_parameters( ) syntax structures in a VPS may be selected for HRDoperations while hrd_parameters( ) syntax structures in an SPS are neverselected. The changes shown above to the semantics of hrd_parameters( )syntax structure clarify that when the hrd_parameters( ) syntaxstructure is included in a SPS, the operation points to which thehrd_parameters( ) syntax structure is applicable may be all operationpoints with OpLayerIdSet identical to TargetDecLayerIdSet. As indicatedabove in the modified general decoding process, if an external means isavailable to set TargetDecLayerIdSet, TargetDecLayerIdSet may bespecified by an external means. Otherwise, if the decoding process isinvoked in a bitstream conformance test, TargetDecLayerIdSet may be theset of layer identifiers of an operation point under test. Otherwise,TargetDecLayerIdSet may contain only one layer identifier (i.e., onlyone value of nuh_reserved_zero_(—)6 bits), which is equal to 0. In oneexample, the external means may be an API that is part of a terminalimplementation and that provides a function to set the value ofTargetDecLayerIdSet. In this example, the terminal implementation maycomprise a decoder implementation and certain functions that are notparts of the decoder implementation.

In this way, a device (such as video encoder 20, video decoder 30,additional device 21, or another device) may select, from among a set ofHRD parameters in a video parameter set and a set of HRD parameters in aSPS, a set of HRD parameters applicable to a particular operation point.In addition, the device may perform, based at least in part on the setof HRD parameters applicable to the particular operation point, abitstream conformance test that tests whether a bitstream subsetassociated with the particular operation point conforms to a videocoding standard.

As indicated in above, section E.2.2 of HEVC Working Draft 8 may bemodified to indicate that when the hrd_parameters( ) syntax structure isincluded in a sequence parameter set, the applicable_operation pointsare all the operation points with OpLayerIdSet identical toTargetDecLayerIdSet. Furthermore, as described above,TargetDecLayerIdSet is set to targetOpLayerIdSet, which contains the setof values of nuh_reserved_zero_(—)6 bits present in the bitstream subsetassociated with TargetOp. TargetOp is the operation point under test ina HRD operation. Furthermore, the HRD operations (e.g., a bitstreamconformance test and a decoder conformance test) may invoke the generaldecoding process.

As explained above, section 8.1 of HEVC Working Draft 8 may be modifiedto provide that the sub-bitstream extraction process as specified insubclause 10.1 is applied with TargetDecHighestTid andTargetDecLayerIdSet as inputs and the output is assigned to a bitstreamreferred to as BitstreamToDecode. Hence, the only values ofnuh_reserved_zero_(—)6 bits present in the BitstreamToDecode are thevalues of nuh_reserved_zero_(—)6 bits in TestDecLayerIdSet (i.e., theset of values of nuh_reserved_zero_(—)6 bits present in the bitstreamsubset associated with TargetOp). Section 8.1 further explains that wheninterpreting the semantics of each syntax element in each NAL unit and“the bitstream” or part thereof (e.g., a coded video sequence) isinvolved, the bitstream or part thereof means BitstreamToDecode or partthereof.

Hence, when interpreting the section describing the semantics of HRDparameters (e.g., section E.2.2 of HEVC Working Draft 8), the term“coded video sequence” means a part of the BitstreamToDecode.TargetDecLayerIdSet is equivalent to the set of all the values ofnuh_reserved_zero_(—)6 bits present in the BitstreamToDecode. It followsthat the phrase in the section describing the semantics of HRDparameters “when the hrd_parameters( ) syntax structure is included in asequence parameter set, the applicable_operation points are all theoperation points with OpLayerIdSet identical to TargetDecLayerIdSet” isequivalent to “when the hrd_parameters( ) syntax structure is includedin a sequence parameter set, the applicable_operation points are all theoperation points with OpLayerIdSet identical to the set of values ofnuh_reserved_zero_(—)6 bits present in the BitstreamToDecode.”

Because a “coded video sequence” is a part of the BitstreamToDecode, theset of nuh_reserved_zero_(—)6 bits present in the coded video sequenceis a subset of the set of nuh_reserved_zero_(—)6 bits present in theBitstreamToDecode. Hence, the phrase “when the hrd_parameters( ) syntaxstructure is included in a sequence parameter set, theapplicable_operation points are all the operation points withOpLayerIdSet identical to the set of values of nuh_reserved_zero_(—)6bits present in the BitstreamToDecode” necessarily entails “when thehrd_parameters( ) syntax structure is included in a sequence parameterset, the applicable_operation points are all the operation points withOpLayerIdSet containing all values of nuh_reserved_zero_(—)6 bitspresent in the coded video sequence.” In other words, if the set ofnuh_reserved_zero_(—)6 bits of an operation point is identical to theset of nuh_reserved_zero_(—)6 bits present in the BitstreamToDecode,then the set of nuh_reserved_zero_(—)6 bits of the operation pointnecessarily contains all nuh_reserved_zero_(—)6 bits values present in acoded video sequence of the BitstreamToDecode. In this phrase, “thecoded video sequence” may refer to a coded video sequence associatedwith the particular SPS.

When performing a HRD operation, the device may determine, from amongthe hrd_parameters( ) syntax structures indicated in a VPS and ahrd_parameters( ) syntax structure indicated in a SPS, a hrd_parameters() syntax structure applicable to TargetOp. A particular hrd_parameters() syntax structure in the VPS is applicable to TargetOp if the layer idset of TargetOp matches a set of layer identifiers specified in the VPSfor the particular hrd_parameters( ) syntax structure. Thehrd_parameters( ) syntax structure in the SPS may be applicable toTargetOp if the layer id set of TargetOp (i.e., TargetDecHighestTid)(i.e., the set of nuh_reserved_zero_(—)6 bits present inBitstreamToDecode) contains all nuh_reserved_zero_(—)6 bits present inthe coded video sequence of the SPS (which is a subset of the set ofnuh_reserved_zero_(—)6 bits in BitstreamToDecode). Because the set ofnuh_reserved_zero_(—)6 bits of TargetOp may necessarily contain allnuh_reserved_zero_(—)6 bits values present in the coded video sequenceassociated with the SPS, the hrd_parameters( ) syntax structure in theSPS may always be applicable to TargetOp. However, not all SPS's havehrd_parameters( ) syntax structures. If a SPS does have anhrd_parameters( ) syntax structure and the set of nuh_reserved_zero_(—)6bits present in BitstreamToDecode contains all nuh_reserved_zero_(—)6bits present in the coded video sequence of the SPS, then thehrd_parameters( ) syntax structure of the SPS should be used. Becausenot all SPS's have hrd_parameters( ) syntax structures, the VPS maystill be selected.

Furthermore, as shown above in modifications to section E.2.2 of HEVCWorking Draft 8, when a device performs a bitstream conformance test,the video decoder may determine that the bitstream does not conform tothe video coding standard when, for all sets of HRD parameters in acoded video sequence, more than one set of HRD parameters applies to thesame operation point. In addition, when the device performs a bitstreamconformance test, the video decoder may determine that the bitstreamdoes not conform to the video coding standard when more than one set ofHRD parameters in the VPS applies to the same operation point.Furthermore, when the device performs the bitstream decoding test, thedevice may determine that the bitstream does not conform to the videocoding standard when the VPS includes a set of HRD parameters thatapplies to operation points having layer id sets containing only thevalue 0.

FIG. 3 is a block diagram illustrating an example video decoder 30 thatis configured to implement the techniques of this disclosure. FIG. 3 isprovided for purposes of explanation and is not limiting on thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video decoder 30 inthe context of HEVC coding. However, the techniques of this disclosuremay be applicable to other coding standards or methods.

In the example of FIG. 3, video decoder 30 includes an entropy decodingunit 150, a prediction processing unit 152, an inverse quantization unit154, an inverse transform processing unit 156, a reconstruction unit158, a filter unit 160, and a decoded picture buffer 162. Predictionprocessing unit 152 includes a motion compensation unit 164 and anintra-prediction processing unit 166. In other examples, video decoder30 may include more, fewer, or different functional components.

A coded picture buffer (CPB) 151 may receive and store encoded videodata (e.g., NAL units) of a bitstream. Entropy decoding unit 150 mayreceive NAL units from CPB 151 and parse the NAL units to decode syntaxelements. Entropy decoding unit 150 may entropy decode entropy-encodedsyntax elements in the NAL units. Prediction processing unit 152,inverse quantization unit 154, inverse transform processing unit 156,reconstruction unit 158, and filter unit 160 may generate decoded videodata based on the syntax elements extracted from the bitstream.

The NAL units of the bitstream may include coded slice NAL units. Aspart of decoding the bitstream, entropy decoding unit 150 may extractand entropy decode syntax elements from the coded slice NAL units. Eachof the coded slices may include a slice header and slice data. The sliceheader may contain syntax elements pertaining to a slice. The syntaxelements in the slice header may include a syntax element thatidentifies a PPS associated with a picture that contains the slice.

In addition to decoding syntax elements from the bitstream, videodecoder 30 may perform a reconstruction operation on a non-partitionedCU. To perform the reconstruction operation on a non-partitioned CU,video decoder 30 may perform a reconstruction operation on each TU ofthe CU. By performing the reconstruction operation for each TU of theCU, video decoder 30 may reconstruct residual blocks of the CU.

As part of performing a reconstruction operation on a TU of a CU,inverse quantization unit 154 may inverse quantize, i.e., de-quantize,coefficient blocks associated with the TU. Inverse quantization unit 154may use a QP value associated with the CU of the TU to determine adegree of quantization and, likewise, a degree of inverse quantizationfor inverse quantization unit 154 to apply. That is, the compressionratio, i.e., the ratio of the number of bits used to represent originalsequence and the compressed one, may be controlled by adjusting thevalue of the QP used when quantizing transform coefficients. Thecompression ratio may also depend on the method of entropy codingemployed.

After inverse quantization unit 154 inverse quantizes a coefficientblock, inverse transform processing unit 156 may apply one or moreinverse transforms to the coefficient block in order to generate aresidual block associated with the TU. For example, inverse transformprocessing unit 156 may apply an inverse DCT, an inverse integertransform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the coefficient block.

If a PU is encoded using intra prediction, intra-prediction processingunit 166 may perform intra prediction to generate predictive blocks forthe PU. Intra-prediction processing unit 166 may use an intra predictionmode to generate the predictive luma, Cb and Cr blocks for the PU basedon the prediction blocks of spatially-neighboring PUs. Intra-predictionprocessing unit 166 may determine the intra prediction mode for the PUbased on one or more syntax elements decoded from the bitstream.

Prediction processing unit 152 may construct a first reference picturelist (RefPicList0) and a second reference picture list (RefPicList1)based on syntax elements extracted from the bitstream. Furthermore, if aPU is encoded using inter prediction, entropy decoding unit 150 mayextract motion information for the PU. Motion compensation unit 164 maydetermine, based on the motion information of the PU, one or morereference regions for the PU. Motion compensation unit 164 may generate,based on samples blocks at the one or more reference blocks for the PU,predictive luma, Cb and Cr blocks for the PU.

Reconstruction unit 158 may use the luma, Cb and Cr transform blocksassociated with TUs of a CU and the predictive luma, Cb and Cr blocks ofthe PUs of the CU, i.e., either intra-prediction data orinter-prediction data, as applicable, to reconstruct the luma, Cb and Crcoding blocks of the CU. For example, reconstruction unit 158 may addsamples of the luma, Cb and Cr transform blocks to corresponding samplesof the predictive luma, Cb and Cr blocks to reconstruct the luma, Cb andCr coding blocks of the CU.

Filter unit 160 may perform a deblocking operation to reduce blockingartifacts associated with the luma, Cb and Cr coding blocks of the CU.Video decoder 30 may store the luma, Cb and Cr coding blocks of the CUin decoded picture buffer 162. Decoded picture buffer 162 may providereference pictures for subsequent motion compensation, intra prediction,and presentation on a display device, such as display device 32 ofFIG. 1. For instance, video decoder 30 may perform, based on the luma,Cb and Cr blocks in decoded picture buffer 162, intra prediction orinter prediction operations on PUs of other CUs. In this way, videodecoder 30 may decode, from the bitstream, transform coefficient levelsof the significant luma coefficient block, inverse quantize thetransform coefficient levels, apply a transform to the transformcoefficient levels to generate a transform block, generate, based atleast in part on the transform block, a coding block, and output thecoding block for display.

FIG. 4 is a flowchart illustrating an example operation 200 of a device,in accordance with one or more techniques of this disclosure. Operation200 may be performed by video encoder 20, video decoder 30, additionaldevice 21, or another device. As illustrated in the example of FIG. 4,the device may select, from among a set of Hypothetical HRD parameters(e.g., hrd_parameters syntax structures) in a VPS and a set of HRDparameters in a SPS, a set of HRD parameters applicable to a particularoperation point of a bitstream (202). In addition, the device mayperform, based at least in part on the set of HRD parameters applicableto the particular operation point, an HRD operation on a bitstreamsubset associated with the particular operation point (204). Forexample, the device may perform a bitstream conformance test or adecoder conformance test.

FIG. 5 is a flowchart illustrating an example operation 250 of a device,in accordance with one or more techniques of this disclosure. Operation200 may be performed by video encoder 20, video decoder 30, additionaldevice 21, or another device. As illustrated in the example of FIG. 5,the device may perform a bitstream conformance test that determineswhether a bitstream conforms to a video coding standard (252). Thedevice may perform a decoding process as part of performing a bitstreamconformance test (254).

As illustrated in the example of FIG. 5, when performing the decodingprocess, the device may perform a bitstream extraction process toextract, from the bitstream, an operation point representation of anoperation point defined by a target set of layer identifiers and atarget highest temporal identifier (256). The target set of layeridentifiers may contain values of layer identifier syntax elementspresent in the operation point representation. The target set of layeridentifiers may be a subset of values of layer identifier syntaxelements of the bitstream. The target highest temporal identifier may beequal to a greatest temporal identifier present in the operation pointrepresentation, the target highest temporal identifier being less thanor equal to a greatest temporal identifier present in the bitstream.Furthermore, the device may decode NAL units of the operation pointrepresentation (258).

FIG. 6 is a flowchart illustrating an example HRD operation 300 of adevice, in accordance with one or more techniques of this disclosure.HRD operation 300 may be performed by video encoder 20, video decoder30, additional device 21, or another device. Other devices may include aconformance bitstream checker that takes a bitstream as input, andoutputs an indication of whether the input bitstream is a conformingbitstream or not. In some examples, HRD operation 300 may determineconformance of a bitstream to a video coding standard. In otherexamples, HRD operation 300 may determine conformance of a decoder to avideo coding standard. As part of performing HRD operation 300, thedevice may determine a highest temporal identifier of a bitstream-subsetassociated with a selected operation point of a bitstream (302). Inaddition, the device may determine, based on the highest temporalidentifier, a particular syntax element from among an array of syntaxelements (e.g., sps_max_num_reorder_pics[i],sps_max_dec_pic_buffering[i], and cpb_cnt_minus1[i]) (304). The devicemay use the particular syntax element in the HRD operation (306).

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over, as oneor more instructions or code, a computer-readable medium and executed bya hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transient media, but areinstead directed to non-transient, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of processing video data, the methodcomprising: performing a hypothetical reference decoder (HRD) operation,wherein the HRD operation determines conformance of a bitstreamcomprising encoded video data to a video coding standard or determinesconformance of a video decoder to the video coding standard, whereinperforming the HRD operation comprises: selecting an operation pointunder test, wherein a highest temporal identifier of a bitstream-subsetassociated with the operation point under test is less than a greatesttemporal identifier present in the bitstream or a target set of layeridentifiers of the bitstream-subset does not include all values of layeridentifier syntax elements of the bitstream; determining, based on thehighest temporal identifier, a first syntax element from among a firstarray of syntax elements in the bitstream, respective syntax elements inthe first array of syntax elements specifying, for respective values ofthe highest temporal identifier, a maximum required size of a decodedpicture buffer (DPB); determining, based on the highest temporalidentifier, a second syntax element from among a second array of syntaxelement in the bitstream, respective syntax elements in the second arrayof syntax elements specifying, for respective values of the highesttemporal identifier, a maximum allowed number of pictures preceding anypicture in decoding order and succeeding that picture in output order;determining, based on the highest temporal identifier, a third syntaxelement from among a third array of syntax element in the bitstream,respective syntax elements in the third array of syntax elementsspecifying, for respective values of the highest temporal identifier,numbers, minus 1, of alternative coded picture buffer (CPB)specifications in the bitstream; and using the first, second, and thirdsyntax elements in the HRD operation.
 2. The method of claim 1, whereinperforming the HRD operation comprises: selecting the operation point;determining a target set of layer identifiers of the operation pointunder test and the highest temporal identifier; selecting a set ofhypothetical reference decoder (HRD) parameters applicable to theoperation point under test; using the selected set of HRD parameters toconfigure a HRD that performs the decoding process; and performing adecoding process.
 3. The method of claim 2, wherein performing thedecoding process comprises decoding, from a sequence parameter set(SPS), the first array of syntax elements; and wherein using the firstsyntax element comprises determining that the bitstream is not inconformance with the video coding standard when a value indicated by thefirst syntax element is greater than a maximum DPB size.
 4. The methodof claim 2, wherein performing the decoding process comprises decoding,from a SPS, the first array of syntax elements; and wherein using thefirst syntax element comprises performing a bumping process that emptiesone or more picture storage buffers of the DPB when a current picture isnot an Instantaneous Decoding Refresh (IDR) picture or a Broken LinkAccess (BLA) picture and the number of pictures in the DPB marked asneeded for output is greater than a value indicated by the first syntaxelement.
 5. The method of claim 2, wherein: wherein performing thedecoding process comprises decoding, from a SPS, the first array ofsyntax elements; and wherein using the first syntax element comprisesperforming a bumping process that empties one or more picture storagebuffers of the DPB when a current picture is not an IDR picture or a BLApicture and the number of pictures in the DPB is indicated by the firstsyntax element.
 6. The method of claim 2, wherein performing thedecoding process comprises decoding, from a SPS, the first array ofsyntax elements, and wherein a number of picture storage buffers in theDPB is indicated by the first syntax element.
 7. The method of claim 2,wherein performing the decoding process comprises: decoding, from an SPSactive for a current picture, the first array of syntax elements;decoding, from an SPS active for a preceding picture, a fourth array ofsyntax elements, wherein each syntax element in the fourth array ofsyntax elements indicates a maximum required size of the DPB of the HRD;and determining, based on the target highest temporal identifier, afourth syntax element in the fourth array; and wherein using the firstsyntax element comprises when the current picture is an IDR picture or aBLA picture and a value indicated by the first syntax element isdifferent than a value indicated by the fourth syntax element, inferringa value of a fifth syntax element regardless of a value indicated by thefifth syntax element, wherein the fifth syntax element specifies howpreviously-decoded pictures in the DPB are treated after decoding of anIDR picture or BLA picture.
 8. The method of claim 2, wherein performingthe decoding process comprises decoding a HRD parameters syntaxstructure that includes the selected set of HRD parameters, wherein theselected set of HRD parameters includes the third array of syntaxelements; and wherein using the third syntax element comprisesdetermining, based at least in part on a scheduler selection index in arange of 0 to a value of the third syntax element, an initial CPBremoval delay of a CPB of the HRD.
 9. The method of claim 2, whereinperforming the decoding process further comprises decoding, from a SPS,the first array of syntax elements; and wherein using the first syntaxelement comprises determining, based at least in part on whether anumber of decoded pictures in the DPB is less than or equal to themaximum of 0 and a value indicated by the first syntax element minus 1,whether the bitstream conforms to the video coding standard.
 10. Adevice comprising one or more processors configured to: perform ahypothetical reference decoder (HRD) operation, wherein the HRDoperation determines conformance of a bitstream comprising encoded videodata to a video coding standard or determines conformance of a videodecoder to the video coding standard, wherein the one or more processorsare configured such that, as part of performing the HRD operation, theone or more processors: select an operation point under test, wherein ahighest temporal identifier of a bitstream-subset associated with theoperation point under test is less than a greatest temporal identifierpresent in the bitstream or a target set of layer identifiers of thebitstream-subset does not include all values of layer identifier syntaxelements of the bitstream; determine, based on the highest temporalidentifier, a first syntax element from among a first array of syntaxelements in the bitstream, respective syntax elements in the first arrayof syntax elements specifying, for respective values of the highesttemporal identifier, a maximum required size of a decoded picture buffer(DPB); determine, based on the highest temporal identifier, a secondsyntax element from among a second array of syntax element in thebitstream, respective syntax elements in the second array of syntaxelements specifying, for respective values of the highest temporalidentifier, a maximum allowed number of pictures preceding any picturein decoding order and succeeding that picture in output order;determine, based on the highest temporal identifier, a third syntaxelement from among a third array of syntax element in the bitstream,respective syntax elements in the third array of syntax elementsspecifying, for respective values of the highest temporal identifier,numbers, minus 1, of alternative coded picture buffer (CPB)specifications in the bitstream; and use the first, second, and thirdsyntax elements in the HRD operation.
 11. The device of claim 10,wherein when the one or more processors perform the HRD operation, theone or more processors: select the operation point under test; determinea target set of layer identifiers of the operation point under test andthe highest temporal identifier; select a set of HRD parametersapplicable to the operation point under test; use the selected set ofHRD parameters to configure a HRD that performs the decoding process;and perform a decoding process.
 12. The device of claim 11, wherein whenthe one or more processors perform the decoding process, the one or moreprocessors decode, from a sequence parameter set (SPS), the first arrayof syntax elements; and wherein when the one or more processors use thefirst syntax element, the one or more processors determine that thebitstream is not in conformance with the video coding standard when avalue indicated by the first syntax element is greater than a maximumDPB size.
 13. The device of claim 11, wherein when the one or moreprocessors perform the decoding process, the one or more processorsdecode, from a SPS, the first array of syntax elements; and wherein whenthe one or more processors use the first syntax element, the one or moreprocessors perform a bumping process that empties one or more picturestorage buffers of the DPB when a current picture is not anInstantaneous Decoding Refresh (IDR) picture or a Broken Link Access(BLA) picture and the number of pictures in the DPB marked as needed foroutput is greater than a value indicated by the first syntax element.14. The device of claim 11, wherein: wherein when the one or moreprocessors perform the decoding process, the one or more processorsdecode, from a SPS, the first array of syntax elements; and wherein whenthe one or more processors use the first syntax element, the one or moreprocessors perform a bumping process that empties one or more picturestorage buffers of the DPB when a current picture is not an IDR pictureor a BLA picture and the number of pictures in the DPB is indicated bythe first syntax element.
 15. The device of claim 11, wherein when theone or more processors perform the decoding process, the one or moreprocessors decode, from a SPS, the first array of syntax elements, andwherein a number of picture storage buffers in the DPB is indicated bythe first syntax element.
 16. The device of claim 11, wherein when theone or more processors perform the decoding process, the one or moreprocessors: decode, from an SPS active for a current picture, the firstarray of syntax elements; decode, from an SPS active for a precedingpicture, a fourth array of syntax elements, wherein each syntax elementin the fourth array of syntax elements indicates a maximum required sizeof the DPB of the HRD; and determine, based on the target highesttemporal identifier, a fourth syntax element in the fourth array; andwherein when the one or more processors use the first syntax element,the one or more processors infer, when the current picture is an IDRpicture or a BLA picture and a value indicated by the first syntaxelement is different than a value indicated by the fourth syntaxelement, a value of a fifth syntax element regardless of a valueindicated by the fifth syntax element, wherein the fifth syntax elementspecifies how previously-decoded pictures in the DPB are treated afterdecoding of an IDR picture or BLA picture.
 17. The device of claim 11,wherein when the one or more processors perform the decoding process,the one or more processors decode a HRD parameters syntax structure thatincludes the selected set of HRD parameters, wherein the selected set ofHRD parameters includes the third array of syntax elements; and whereinwhen the one or more processors use the third syntax element, the one ormore processors determine, based at least in part on a schedulerselection index in a range of 0 to a value of the third syntax element,an initial CPB removal delay of a CPB of the HRD.
 18. The device ofclaim 11, wherein when the one or more processors perform the decodingprocess, the one or more processors decode, from a SPS, the first arrayof syntax elements; and wherein when the one or more processors use thefirst syntax element, the one or more processors determine, based atleast in part on whether a number of decoded pictures in the DPB is lessthan or equal to the maximum of 0 and a value indicated by the firstsyntax element minus 1, whether the bitstream conforms to the videocoding standard.
 19. A device comprising: means for performing ahypothetical reference decoder (HRD) operation, wherein the HRDoperation determines conformance of a bitstream comprising encoded videodata to a video coding standard or determines conformance of a videodecoder to the video coding standard, wherein the means for performingthe HRD operation comprises: means for selecting an operation pointunder test, wherein a highest temporal identifier of a bitstream-subsetassociated with the operation point under test is less than a greatesttemporal identifier present in the bitstream or a target set of layeridentifiers of the bitstream-subset does not include all values of layeridentifier syntax elements of the bitstream; means for determining,based on the highest temporal identifier, a first syntax element fromamong a first array of syntax elements in the bitstream, respectivesyntax elements in the first array of syntax elements specifying, forrespective values of the highest temporal identifier, a maximum requiredsize of a decoded picture buffer (DPB); means for determining, based onthe highest temporal identifier, a second syntax element from among asecond array of syntax element in the bitstream, respective syntaxelements in the second array of syntax elements specifying, forrespective values of the highest temporal identifier, a maximum allowednumber of pictures preceding any picture in decoding order andsucceeding that picture in output order; means for determining, based onthe highest temporal identifier, a third syntax element from among athird array of syntax element in the bitstream, respective syntaxelements in the third array of syntax elements specifying, forrespective values of the highest temporal identifier, numbers, minus 1,of alternative coded picture buffer (CPB) specifications in thebitstream; and means for using the first, second, and third syntaxelements in the HRD operation.
 20. A non-transitory computer-readablestorage medium having instructions stored thereon that, when executed byone or more processors of a device, configure the device to perform ahypothetical reference decoder (HRD) operation, wherein the HRDoperation determines conformance of a bitstream comprising encoded videodata to a video coding standard or determines conformance of a videodecoder to the video coding standard, wherein execution of theinstructions configure the one or more processor such that, as part ofperforming the HRD operation, the one or more processors: select anoperation point under test, wherein a highest temporal identifier of abitstream-subset associated with the operation point under test is lessthan a greatest temporal identifier present in the bitstream or a targetset of layer identifiers of the bitstream-subset does not include allvalues of layer identifier syntax elements of the bitstream; determine,based on the highest temporal identifier, a first syntax element fromamong a first array of syntax elements in the bitstream, respectivesyntax elements in the first array of syntax elements specifying, forrespective values of the highest temporal identifier, a maximum requiredsize of a decoded picture buffer (DPB); determine, based on the highesttemporal identifier, a second syntax element from among a second arrayof syntax element in the bitstream, respective syntax elements in thesecond array of syntax elements specifying, for respective values of thehighest temporal identifier, a maximum allowed number of picturespreceding any picture in decoding order and succeeding that picture inoutput order; determine, based on the highest temporal identifier, athird syntax element from among a third array of syntax element in thebitstream, respective syntax elements in the third array of syntaxelements specifying, for respective values of the highest temporalidentifier, numbers, minus 1, of alternative coded picture buffer (CPB)specifications in the bitstream; and use the first, second, and thirdsyntax elements in the HRD operation.